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The glacial drifts of Norfolk
OLD HAVEN PEBBLE-BEDS AT CATERHAM.
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would fall from a cliff. In that case it would rest upon the pebbles at the base of the cliff, and although much of the mass would be either ground down into pebbles or washed away, its nucleus would be occasionally preserved unmodified, and surrounded on all sides by the well-rounded pebble-beds. THE GLACIAL DRIFTS OF NORFOLK. By HORACE B. WOODWARD, F.G.S., of the Geological Survey of England. The subject of the Glacial Drifts, unfortunately, is by no means adapted for ready writing nor calculated to excite great enthusiasm j for the subdivisions of the beds are a fertile source of discussion, and there is no agreement whatever about their method of formation. The Drifts do not" behave" like other and older formations, for although they may occur regularly for a few miles-Boulder Clay over Sand or Gravel-on the borders of a valley, yet all at once the Clay plunges to the lowest level of the ground, in defiance of geological rules. You may find a Clay-pit in one field and a deep gravel-pit in the next, and this without the change we are taught to expect in the form of the ground; and, sometimes, where the pits are but few yards apart, it may be difficult to determine the newer deposit. The ordinary tests for identifying or distinguishing strata furnish little help to the student of the Norfolk Drifts. The fossils found in them are either certainly derived, or more or less fragmentary and probably derived. The lithological characters of the strata are variable, while the same general characters are repeated in successive accumulations, so that local peculiarities can be taken as guides only by those who work gradually over a district from pit to pit. Even stratigraphical succession affords no sure means of identification, for lenticular beds of sand or gravel occur in both Upper and Lower Boulder Clay; and the evidence of erratic blocks, although useful, is no infallible clue, as one may often search the Boulder Clay in vain for other stones than Chalk and flint. After spending about a year in Norfolk I began to believe I knew all about the Drifts, but during the following seven years of my sojourn in that county, as I moved from place to place, I somehow seemed to know less and less; and I cannot say what would
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have been the result, but fortunately the Geological Survey of tbe county came to an end. While in Norfolk, I was more than once asked to give such a description of the Glacial bcds, that from it anyone could go into the field and recognize the several divisions. Tbis is a request with which I never felt able to comply. Distance, however, lends enchantment to the view, anu if I strive to give my notions of these Drifts, now that I am :\way from their perplexing details, perhaps my remarks may possess more value than if they were written on the spot. Two questions come before us. What is the broad general grouping of the beds? Wl!at is the story they tell? If I succeed in answering these questions, and in extracting some hnrmony from the accompanying sections, my task lllay not be in vain; and although I do not wish to neglect the opinions of others, I need not attempt a statemen"t of all the conflicting views on Norfolk Drifts which a study of the literature woulu supply; for such a proceeding would extend my paper to undue length, and the result woulu he simply bewiluering. Broadly speaking the Drifts admit of two divisions, each of which locally contains many kinds of marl, clay, loam, sand, and gravel. The Lower division (or Lower Glacial) is well shown in the cliffs between \,yeyhoQrn and Happisburgh. It comprises the Cromer Till, and the Contorted Drift with interbedded and over~ lying (Middle Glacial) sands and gravels. These beds form the main mass of the celebrated" mud cliffs" of Norfolk. The Cromer Till is a tough bluisb"grey unstratified Boulder Clay, containing fragments of l'ellina Balthica, .Jlya arenaria, Cardium edule, and Cyprina Tslandica. It contains also many glaciated fragments of Chalk and flint, of septaria (probably from tbe Kimeridge Clay), and Carboniferous Limestone; as well as many igneous and metamorpbic rocks, such as mica-schist, granite, felstone, basalt, &c. In tbis Till fine examples of glaciated stones are more abundanttban in any otber Drift in Norfolk. Overlying tbe Till come thick beds of brown loam, chalky clay, gravel, and sand, which in many places are so twisted and di~ t.ubed, that tbe name Contorted Drift was applied to them. It is in fact a conglomeration of all kinds of sediments, although loam and marl preuominatc. Among the remarkable features of this
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Contorted Drift are the large boulders which it contains, not merely those of quartzite, grit, gneiss, granite, and basalt, of which blocks measuring over 6 feet in length have sometimes been found; but huge boulders of Chalk-with-flints, one re-deposited mass 01' rather strip of which is upwards of 180 yards in length. Above the Contorted Drift come the sands and gravels ca11ed " Middle GlaciaL" The sands in places contain what may be termed shoals of broken shells, and these, more conspicuous in the cliffs of Gorleston and Cortou, between Yarmouth and Lowestoft, were noticed by the earlier geologists as re-deposited Crag sheUs. By searching the cliffs and sifting loads of the material, sent' home to them in sacks, Messrs. Wood and Harmer were enabled to give a list of over 100 species'*' of mo11usca from these sands. The assemblage is a very curious one. With the exception of one Venus, a LOI'l}II'S, and some new species, a11 the shells are found in our Crag deposits; and it is very natural to suppose that they were derived from them; but while coutaining a number of species which might have come out of the Corallinc Crag, and others that might have been derived from the Red and Norwich Crags, yct" not a trace or fragment of most of the common strong sheUs of the Coralline and Red Crags has occurred." Nearly aU the specimens found, it is true, are more or less rolled, but fragile shells like Anomia ephippium are occasionally preserved. Messrs. Wood and Harmer conclude that the fauna was contemporaneous, although the she11s bear evidence of having been shifted and rolled by currents which brought them from some other part of the seabottom; while in their opinion some of the delicate shells may have been transported by floating masses such as seaweed. These conclusions I believe first started the notion of Interglacial mild periods-for the presence of Coralline Crag forms suggested that somc connection with the Mediterranean area had been reopened by submergence of the land at this period. Mr. Clement Reid, who has carefully examined the sheUs found in the Glacial sands of the Cromer Cliffs, remarks :-" There has been much discussion as to the contemporaneous or derivative origin of the 'Middle Glacial' fauna, and it is interesting to trace in a new district the same peculiarities in the fossils which led Mr. S. V. Wood to consider the fauna to be contemporaneous with the deposit. It is not improbable that a large proportion of the fragments of the 'I<
See 'Supplements to the Crag Mollusca.'-Palmontograph. Soc.
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common shells may be derivative; but near Cromer, as at Yarmouth, the peculiar and characteristic types are the most perfect. Though the commonest forms are Tellina Balthica, Cardium edule, Cyprina Islandica, and Mya a/'enaria, of the last three nothing but small fragments were seen, and of Tellina Balthica only a few nearly perfect valves; but the single specimens of Nassa reticosa, Anomia, and Dentalium w"ere nearly perfect, as were two or three of Scalm'ia G1'GJnlandica and Natica Grceniandica? The re-appearance of Crag forms may be explained by the submergence of the land to a greater extent than had occurred since the time of the Coralline Crag, thus re-opening the connection with the southern seas, and allowing species long exterminated in this area to again migrate into it." * I dwell at some length on this subject, because it is a very important one, and because I have for some time felt great doubt about the shell fauna being contemporaneous. Of course the aspect of thp, beds alone makes one sceptical, and it is admitted that the shells did not live on the spots where they have been accumulated. It may be remarked that, traced southwards, these so-called Middle Glacial Sands pass mostly into gravels. which underlie the Chalky Bonlder Clay over a considerable part of Essex, and that only in two or three places in Suffolk, sonth of Corton, have fragments of Crag shells been found in the Drift of this portion of the eastern counties. Moreover, near Hertford and other places, seams of Boulder Clay have been met with in gravel beneath the main mass of Chalky Boulder Clay-which gravel has been grouped as Middle Glacial by Mr. Wood himself, t and this does not support the view of a much milder climate. Regarding the shells as mainly derived from the Crag deposits, the question arises where are (or where were) the beds whence the shells were obtained? For the Coralline and Red Crags are exposed only to the south of the tracts, where we meet with these fossiliferous Glacial sands. In 1860 Mr. T. F. Jamieson described some beds of sand and gravel on the eastern border of AberJeenshire, which contained fragments of shells, belonging to Crag species. At that time he
* . Geology of the Coun try around Cromer' (' Geol. Survey'), pp. 93, 94. t See' Guide to the Geology of London.' By W. Whitaker. 4th Edition, 1884, p. 62.
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thought that some part, at least, of the gravel itself, might be a Preglacial deposit of Crag age. Three years ago, however, Mr. Jamieson brought forward further information respecting these deposits. He had ascertained that what appears to be a Glacial bed underlies them, and he now believes that in their present state these accumnlations are all of more recent origin than their fossil contents would indicate. * However, the important part of the subject is that the shell fragments comprise forms found in the Coralline, Red, and Norwich Crags, as well as in more recent deposits, although all of the species, excepting Tellina Balthica, occur in the Red Crag. The absence of Tellina obliqlta, so common in our Norwich and Red Crags, is noteworthy j but the occurrence in Aberdeenshire of C!JjJl'ina 1'Ustica, large forms of Pectunculus glycimel'is, of Venus casina, and of Voluta Lambe1·ti, strongly suggest their derivation in part from deposits of the age of the Coralline Crag, and this is Mr. Jamieson's opinion. I mention these facts to show that Oldel' Pliocene, as well as Newer Pliocene accumulations, took place so far north as Aberdeenshire; and hence all difficulty is removed in seeking a northern derivation for the shell accumulations in the so-called "Middle Glacial" Sands of East Anglia. Moreover, local geographical distribution of the mollusca in the Crag pcriod may account for the peculiarities in the fauna. The so-called Middle Glacial Sands are intimately connected with the Contorted Drift; their gravelly equivalents in the south do not indicate deeper water conditions, nor have we any southerly fossiliferolls beds of this age, which we might expect had the fauna migrated in Interglacial times from the Mediterranean area. Hence, we are justified in regarding the question, at any rate, as an open one, and in ma1dng the suggestion that the Middle Glacial Shells may have been largely derived from old Crag accumulations, now entirely destroyed or buried up beneath the waters of the North Sea. It is right to mention that Messrs. Wood and Harmer have expressed their opinion that the Contorted Drift was overlaid unconformably by these Middle Glacial Sands and Gravels, and that during the interval between them the valley system of East Anglia was marked out. This is not borne out by the evidence furnished in the coast-sections, for, as Mr. Reid has shown, the
* . Qnart. Jonrn. Geol. Soc.,' Vol. xxxviii, p. 145.
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basin-shaped hollows in which the sands and gravels frequently lie, are due to contortion, and not to erosion. Where anything like unconformity exists, it is where these gravels and sands have been rearranged, and such appears to be the case near Blakeney, in Norfolk, where these reconstructed gravels have assumed the form of Eskers. They are probably of later Glacial age, and may perhaps be grouped with the Cannon-shot gravels to be mentioned presently. Mr. T. V. Holmes has described the peculiarities of these Eskers. '*' We thus have in the Cromer Cliffs evidence in descending order of sand and gravel, loamy beds (Contorted Drift, &c.), and Till or Lower Boulder Clay. This order is maintained over a good part of north-east Norfolk; and as the loamy beds are prevalent in the low grounds, and the sands and gravels overlying them form the hills, the geology seems fairly simple. The Geological Survey Map, indeed, shows the general strncture, gravel and sand (coloured pink) resting on loam or brickearth (coloured yellow). Passing westwacds the loam contains huge masses or jambs (as they are called) of marl or chalky clay, and these, where sufficiently prominent and extensive, are marked on the map with the same tint as Upper or Chalky Boulder Clay (blue). Still further west the main mass of the Drift bcneath the sand and gravel is chalky or marly; consequently the map is to a very large extent coloured blue, with patches only of yellow, where brickearth or loam is developed. The real fact of the case is, that the Lower Glacial Clays, which, east of Cromer and near Norwich, consist chiefly of brown stony loam, become westwards so like the Chalky Boulder Clay, that no one, from the evidence of pit sections, could tell one from the other. As a rule, the Lower Glacial Drifts rest on a very even surface of the Forest Bed Series, which consists of sands, gravels, and laminated clays. Mr. Reid mentions, however, that in places where the Till rests on laminated clays, the beds have been slightly crumpled. The Cromer Till may be regarded as the product of an ice-sheet, deriving its shell-fragments from the bed of tIle sea or from preglacial deposits over which the material was pushed. Submergence
* 'Proc. Norwich Geol. Soc.,' Vol. i, p. 263, and' Geol. Mag.,' Decade II. Vol. x, p. 438. See also' Geology of the Country around Fakenham,' &c, (' Geol. Survey'), p. 35.
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following, the succeeding Contorted Drift, which exhibits evidence of stratification and sometimes of ripple-marks, was probably deposited in the sea; while some of the large blocks of igneous and metamorphic rocks may have been brought by ice-bergs, perhaps from the Scandinavian area. Sands and gravel£; succeeded the more muddy sediments, and these deposits were subsequently acted upon by a force sufficient to produce the violent contortions before mentioned; but before attempting to explain these contortions we must turn to the next deposit. Spreading over a great part of South Norfolk, and over much of Suffolk, extending to the northern margin of the Thames Valley near Brentwood and Epping, and well known, too, at Finchley, is an accumulation of more or less chalky clay, clay containing groundup chalk and chalk stones in abundance, together with flints, and flint pebbles, and also a variety of rocks and derived fossils. Of these, Oolitic material is conspicuous, and the great clay formations, like the Lias, the Oxford Clay, and the Kimeridge Clay, appeal' to have suffered more in the formation of this Boulder Clay than the Oolitic limestones which usually intervene between them. Among the fossils we find Gryph(fJa inc'Ul'va, .wyacites, Gryph(fJa dilatata, and Belemnites abbreviatus. The character of this deposit is fairly uniform over a large area, but while spread out in extensive sheets over the higher grounds of South Norfolk, Suffolk, and Essex, it l'ests now on sand, sometimes on loam, and occasionally on the Norwich Crag, and often it descends to the bottom of the valleys on a level with the Alluvium. The distribution of this Upper 01' Chalky Boulder Clay in Norfolk is very remarkable. One sheet of the Geological Survey Map south of Norwich (66 S.E.), is nearly covcred with it, whereas the sbeet to the north (66 N.E.) is mostly covered with the loam called Contorted Drift, and classed with the Lower Glacial. A glance at the two maps naturally suggests that the two accumulations are varieties of one Boulder Clay, and I may say I have at times held to this view; for over the greater part of the area where the Chalky Clay is developed, there is very little of the Lower Boulder Clay beneath it. The sequence of Upper, Middle and Lower Glacial is the exception and not the rule. We have, it is true, the section at Corton, where Joshua Trimmer, first pointed to the evidence of an Upper and Lower Boulder Clay, but here the Lower Boulder Clay is a very feeble and irregular ac-
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WOODWARD ON THE
cumulation compared with the Lower Glacial Clays at Happisburgh and Cromer; and it is open to question whether the brown stony loam there represents the Cromer Till or a portion of the Contorted Drift; but from the character of the Boulders noted by my colleague, Mr. J. H. Blake, in the Corton Lower Boulder Clay, I should regard it as belonging to the Contorted Drift.'" In this case the Cromer Till is only a very local deposit, and Mr. Reid does not even identify it at Cromer. We may build up ollr sequence, however, by passing from Corton to Happisburgh, regarding (as Messrs. Wood and Harmer have done) the sands on top of the Cromer Cliffs as the same as those at Corton j but, to say the least of it, it is unfortunate that we have no evidence anywhere along the Cromer Cliffs of the Upper or Chalky Boulder Clay. Inland there are a few pit-sections which show the sequence of Chalky Boulder Clay, sand, and stony loam or Lower Boulder Clay; but most of these sections show in the same pit the sand tapering away, and then the two Boulder Clays come together, and their separation is not a happy task. Fortunately in East Norfolk the Lower Clay maintains its character of a brown stony loam, so that whenever a section is exposed, it may usually be distinguished from the more chalky Upper Boulder Clay in that area. It was my duty to map a considerable portion of West Norfolk around Fakenham and Wells, and I had to join up from this area with another tract I had surveyed to the east around Aylsham and North Walsham. At Fakenham I commenced mapping Boulder Clay which presented all the characteristics ofthe Chalky Boulder Clay, and as I Havelled eastwards it appeared to merge into the formation I had there grollped with the Contorted Drift. I could not help it, although I felt sorely grieved and perplexed. The mere separation of clay or marl from sand and gravel was not in itself a very troublesome process, but to try and discriminate Upper and Middle and Lower Glacial deposits taxed my equanimity to the utmost. When the mapping was accomplished the map looked so simple, a foundation of clay with patches of gravel and sand on i~, that no one could sympathize with my many anxieties and doubts; but when I came to write the description, then, as your President re-
* See Sheet 128, 'Horizontal Sections'
(' Geol. Survey').
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marked, and justly too, the explanation seemed far more complicated than the map it was intended to elucidate! "" If you glance at the Cromer map, you can judge how little the surface geology, as there depicted, tells of the great contortions which are so conspicuous in the cliffs. My case was similar. Nearly every good section showed that the beds were very much disturbed. Many railway-cuttings have been made (more to the interest of geologists, I fear, than to the shareholders in the companies) and these cuttings almost invariably displayed the irregularities of the strata; so that I frequently felt that the cuttings added to, rather than diminished, the difficulties of mapping, for they showed how impossible it was to be minutely accurate. For instance, on comparatively low ground, where the general surface evidence indicated clay, and the bordering hills were clearly sand and gravel, with a marked feature, the cuttings would show not merely loam and marl and boulder clay jumbled up together, but large included beds of sand and gravel. Hence a sand or gravel-pit might be opened in the midst of a tract marked as clay on the map, when of the existence of such material there would be no surface evidence. Consequently any written explanation of the district must naturally make the geology seem much more complicated, as it really is, than it appears to be on the map. However, I frequently sought comfort in the Cromer Cliffs, feeling that the contemplation of such a contorted, tumbled, higg-Iedy-piggledy arrangement of beds was enough to confound any field-geologist who wonld attempt to map out the strata t in great detail. It is told of Dr. Buckland that, when travelling in the Eastern Counties, he knew when he was on the Boulder Clay by the rosy cheeks of the lasses; but that I fear would be evidence on which the geological surveyor could not wisely rely, if it be not a libel on other subsoils. My chief difficulty, in reality, arose from trying to separate the Upper Chalky Boulder Clay from the Lower Boulder Clay, which in West Norfolk becomes as a rule more chalky than the bed above; and in the end I had to give up attempting to draw a line, which could not be defined with any approach to accuracy. The difficulty in colouring the maps was obviated by commencing to colonr blue the marl masses which occur in the loamy Conto~ted Drift, and
* See t
'Geology of the Country around Fakenham,' &0. See Sheet 127, 'Horizontal Sections' (I Geol. Survey'), by C. Reid.
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when the marl predominated colouring the whole of it blue, like the Chalky Boulder Clay. Although the term Contorted Drift is usually confined to the Lower Glacial Beds, yet similar contortions also affect the Chalk and sometimes the Norwich Crag. On the Cromer coast we find that the oontortions decrease in intensity as we proceed in an easterly direction j for while at Sherringham and Cromer the disturbances are violent in the extreme, at Happisburgh the beds are little if at all disturbed. The conclusion to which Mr. Reid and myself came, was that the contortions were produced by the agent which formed the Chalky Boulder Clay, and this view was, I believe, first suggested by Mr. S. B. J. Skertchly. Sometimes this Boulder Clay rests on a substratum that shows little or no disturbance. The cliff-sections at Kessingland and Corton, in Suffolk, furnish examples. The clay rests on sand, and As is the rule with such the junction is well-marked all along. junctions, the lower part of the Boulder Clay is sandy, and the line of division, though sometimes undulating, is distinct. Where the Boulder Clay rests on clay, the same distinct line may also be observed; but almost invariably where the underlying clay contains streaks or nests of sand, these are very much contorted. The fact is that the clay without these nests of sand would not well exhibit the contortions j while where sand alone is seen under the Boulder Clay, contortions may be absent because the deposit was of too yielding a nature to be acted upon. In one or two localities where marked lines of bedding occur in the sand, I have, however, found evidencl's of disturbance. On the whole, my experience is that the beds beneath the Boulder Clay of Norfolk are more frequently contorted than not, and that the agent which formed the Chalky Boulder Clay. was instrumental in disturbing the strata over ·which this clay was accumulated. This is an assertion which I do not think anyone acquainted with the country would dispute. What the agent was is another matter, and there, unfortunately, the principal observers agree to differ. In studying the junctions of Boulder Clay with various deposits on which it rests, we sometimes find, as in W est Norfolk, that on the Chalk the line of demarcation is most obscure. It is difficult to say where the Chalk ends and the Boulder Clay begins. In
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these cases it appears evident that the Glacial Drift was formed chiefly from the Ohalk of the district. In this way we may account for some of the very marly varieties of the Boulder Olay, which in places are little else than ground-up Ohalk. Analysis of one of these chalky drifts, blunt for lime near Holt, showed 91 per cent. of carbonate of lime, and the Rev. O. Fisher has spoken of such drift as "an ancient manufacture of ' whiting' on a magnificent scale."* Mr. Reid observes that "The masses of reconstructed Ohalk so common in the Contorted Drift are probably nothing but a later stage of the transported boulders, in this case so shattered and mixed with clay that they form a sort of transition to an ordinary Boulder Olay. From the very marly character of the Oontorted Drift when traced westward, it seems not improbable that that portion of the deposit is continuous with, and passes laterally into, the Great Ohalky Boulder Olay. The general structure of Norfolk and Suffolk appears to show that the whole of tbe contortions are of one age, that of the greatcst glaciation, or of the Great Ohalky Boulder Olay, and it is probably to this period that the disturbances on tbe coast may be referred." t These remarks furnish a comforting explanation of the difficulties met with in thc country around Fakenham. There, where the later Boulder Olay passed directly over the clayey Lower Glacial beds, it no doubt became incorporated with them, causing one contorted mass, and we cannot separate the two deposits. In other places we find the flint-layers of tbe Ohalk disturbed, as if that rock had offered a local impediment, perhaps a low hill or cliff against which the icy agent impinged. Mr. Reid bas explained the flexures in tbe Ohalk at Trimingham as due to glacial action in the form of an ice-sheet. Mr. S. V. Wood previously caUed attention to disturbances in tbe Obalk at Litcham, which he attributed to tbe passage of a glacier over the surface of the rock; and when the Geologists' Association came to Norwich tbe members visited a pit at Trowse, where I pointed out the Ohal k uptilted and underlaid by Boulder Drift; so that tbe disturbance was evidently due to glacial agency. I have since described some sections near 'Veils, where the Ohalk is .. See ' Geology of Fakenham,' &0., p. 23. t ' Geology of the Country around Cromer,' pp. 115-117.
VOL. IX., No.3.
10
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similarly disturbed in connection with the Glacial Drift.- These disturbances of the Chalk help us to explain how the huge isolated masses, or "boulders," of the rock may have been formed. The occurrence of such large shifted rocks in Drift is not confined to Norfolk, for there is an immense mass of detached Chalk in the well-known pit called Roslyn Hole, near Ely, and great boulders of Inferior Oolite and Marlstone occur in the Drift of Lincolnshire. In West Norfolk too there is one celebrated stone called the Merton Boulder, which measures nearly 12 feet in length, with a thickness and breadth of about four or five feet. The derivation of this rock was long a puzzle to Norfolk geologists, until Mr. Whitaker identified it as a Neocomian sandstone of local deriva. tion·t No doubt the Chalk at Trimingham furnishes the most striking evidence of the formation of these huge boulders. Mr. Reid remarks: "If the ice-sheet, instead of flowing over the beds, happens to plough into 01' abut against them, it would bend up a boss of Chalk, as at Beeston. A more extensive disturbance, like that at Trimingham, drives before it a long ridge of the beds, and nips up the Chalk till, like a cloth creased by the sliding of a heavy book, it is folded into an inverted anticlinal. A slight increase of pressure, and the third stage is reached-the top of the anticlinal being entirely sheared off, the Chalk boulder driven up an incline, and forced into the overlying Boulder Clays."t With this view I coincide. It will not, however, be imagined that this is the only explanation that has been given of the phenomena, for when there is room for diversity of opinion geologists fully avail themselves of it. Icebergs have been considered as the agents for transporting the boulders; and Mr. Mellard Reade believes that they were severed from old cliffs by the expansive force of ice in fissures, and then shifted by coast-ice. § I cannot, however, attempt to discuss the various explanations that have been given of the formation of our Glacial Drifts. The agents concerned in their formation may be land-ice, coast-ice, and icebergs; and it is not always possible to '" 'Proc. Geol. Assoc.,' Vol. v, p. 513; 'Geology of Country around Norwich,' p. 135; • Geology of Country a"ound Fakenham,' pp. 9, 2-1. t • Geology of Country around Attleborough,' &c., by F. J. Bennett, p.10. t 'Geology of ·the Country around Cromer,' p. 115. § • Quart. Journ. Geol. Soc.', Vol. xxxviii, p. :122.
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localize their action. Unfortunately, we have very little information concerning what kinds of accnmulations are being formed by landice in the arctic regions. There the icy agents can be studied; but the effects are not, as a rule, so conspicuons. In Norfolk we see the results, and have to infer what were the agents. In the formation of our Chalky Boulder Clay, however, icebergs are generally admitted to have had little or no influence, for the ice from which the floating masses would be severed must have passed over considerable tracts of Chalk, and the Chalk would have been submerged if the icebergs were to have fair play. Mr. Wood advocated the view that the Chalky Boulder Clay was extruded at the foot of an ice-sheet that enveloped the Yorkshire and Lincolnshire Wolds; but the general absence of stratification goes against the view of this clay having been for the most part deposited under water. We require, too, an agent capable of exerting a comparatively uniform influence over wide tracts, of abrading and pushing on material in a manner more extensive than could be attributed to coast-ice, althongh this view of its formation has met with a warm advocate in Mr. Jukes-Browne. Moreover, the Clay has been much compressed, and is so tough and hard in places that navvies engaged in making railway-cuttings have told me they never had a more troublesome material to deal with. The occurrence of the chalk lumps in the clay may perhaps be accounted for in the following way. The surface of the Chalk in Norfolk, along the sea-margin, and in places inland, is seen to have weathered in a very rubbly form, to a depth sometimes of six or eight feet. Frost and rains have no doubt been the chief influences in producing this; and this weathered Chalk would furnish " ready made" the very material for the Chalky Boulder Clay, which consists so largely of lumps of Chalk which have not necessarily been rounded by rolling. Mr. F. J. Bennett, too, has suggested that much of the material of which Boulder Clay was formed may have been the soils or subaerial debris on the surfaces of the land over which the ice passed. This is a subject well deserving of careful study, and it has been discussed in some of the publications of the United States Geological Survey. II II 'Proc. Norwich Geol. Soo.,' Vol. i, p. 256. Geology,' ed. 2, pp. 325, 894.
See also A. Geikie, 'Text of
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If. R. WOODWARD ON THE
One other depol>it must be mentioned. Scattered over the high grounds of Holt and Cromer, and resting on the Chalky Boulder Clay in many places in W est Norfolk, and near Norwich, are great accumulations of coarse boulder gravel-gravel containing large blocks of flint and even paramoudras, all more or less rolled and knocked about. Some few igneous rocIrs occur also, as well lis pebbles of quartz and quartzite. To these deposit.s the name Cannon-shot gravel was applied by Mr. Wood, because the majority of the stones in some places are lC rolled into the shape and dimensions of the now obsolete cannon"hot of from 121bs. to 321bs. calibre." The deposit seems to be intimately connected with the Chalky Boulder Clay, and Messrs. 'Vool! and Harmer have attributed the origin of these gravels to some local modification of this deposit by powerful currents. It is, indeed, an ~ecnmulation that bears eviLIenee of having been formed in a tumultuous way, but the Chalky Clay itself does not yield such large flint boulders in abundance. The question is, whence came the flints-for the deposit is not often found directly on the Chalk, otherwise we might account for it by ordinary marine action 011 a foreshore of that formation. I have ventured to suggest that during later Eocene and Miocene times accumulations of flints might have been formed by subaerial action on the Chalk surfaces of West Norfolk, and that in Glacial times they furnished material for the gravels. * In West Norfolk, where the Chalk bills are covered by straggling outliers of Boulder Clay and gravel, the Lower Drifts are probably not represented. The conclusion that might be drawn from these remarks is that, after all, the divisions of the Drift possess little more than local value. It might also be concluded that, while the work on the Geological Survey is generally considered to be olle of the most delightful of occupations (by those who have had no experience of it), yet to be engaged in NorfoUr trying to distinguish and separate gravels and Boulder Clays, and to say whether there is Uppel' and Middle and Lower Glacial, and, if so, which is whicb,-often while a keen east wind is blowing-is not an enviable situation, and enthusiasm may then langui8h. Olle is sometimes tempted to exclaim that anyone who wished to bave a clear and definite notion of the succession of Norfolk Drifts should confine his attention to certain sections. If he
* 'Trans. Norfolk Nat. Soc.', Vol
iii, pp. 444, 447.
GLACIAL DRIFTS OF NORFOLK.
125
wished to feel confident of the triple division, one series of sections should be visited; if a twofold division would better agree with his notions, other sections might be selected, and so on. My own opinion respecting the Drifts has fluctnated, according to different districts which I have been called upon to examine; and yet probably no district furnishes better sections of the Glacial Drifts than are to be found in Norfolk. Looking at the beds, as we have tried to do, in a general way, we discern that two great divisions may be recognized-the Cromer Till and Contorted Drift, gronped together as Lower Boulder Clay, followed by sands and gravels; and the Chalky or Upper Boulder Clay, with associated sands and gravels. The Lower Boulder Clay, as Mr. John Gunn has remarked, is characterized by boulders of an igneous type, and it often contains Pleistocene shell-fragments. It may have been derived from the Ilorth and north-east. The Upper Boulder Clay is characterized by .Jurassic detritus, and was probably derived from the north-west. But the most important distinction, perhaps, is in the disturbances to which the Lower Glacial Beds have been subjected by the agent which formed the Chalky Boulder Clay. Anyone who wishes for details may consult the Geological Survey Memoirs on portions of Norfolk, in which most of the sections are described, and in which as much detail will be found as the most ardent geologist could desire j while those who wish to study the theoretical questions connected with the Drifts will find ample material in the Inany papers by Messrs. Wood and Harmer. '" It is only right to say that their admirable geological map of the Crag district is in all essential particulars substantiated by the more detailed lllap of the Geological Survey.t Turning now to another subject, the occurrence of Palreolithic implements is a topic that cannot be neglected in any account of the Glacial Drifts of Norfolk. Some years ago now-it Was in 1876-Ml'. S. B. J. Skertchly announced his discovery of flint-implements beneath the Boulder Clay of East Anglia.t I do not wish to enter into all the parti-
* For a Bibliography of Norfolk Geology, Bee the Geological Survey , Memoir on the Country arouud Norwich.' t See' Supplement to the Crag Mollusca' Part i. 1872. ::: ' Geol. :Mag' Dec. IL, Vol. iii, p. 476; see also 'Manufacture of GunHints' (' Geol. Survey'), p. 65; and Prof. J. Geikie's 'Great lee Age,' Ed. 2, p. 565.
126
H. B. WOODWARD ON THE
cuI aI'S of this announcement. Unfortunately the evidence upon which Mr. Skertchly based his conclusions has not been published in detail, and they therefore cannot be tested and verified in the way in which it is desirable that all discoveries shonld be treated; but, after seeing many of the sections with him, I had occasion to deliver an address before the Norwich Geological Society, and then stated that" The interval between the Upper and the Middle and Lower Glacial Beds is probably marked by the Brandon Beds, which Mr. Skertchly has shown to contain our earliest records of man's existence in this country."· The story of my conversion is briefly this: The first time I went, I saw certain sections, and came away unconvinced, nay sceptical. On the second occasion, I saw other sections, and one in particular at a brickyard near Mildenhall. Here there was brickearth, clearly overlaid by Boulder Clay,' and Mr. Skertchly informed me that Palreolithic implements had been fonnd in this brickearth. It is true I found no implements, nor did he find one while I was there; but there was no escape from the co"nclusion that the brickearth was older than the Boulder Clay. This bed of brickearth, and other beds of brickearth near Thetford, interested me much, for I had come across similar beds near Norwich, which were older than the Boulder Clay. These I diligently searched for flint-implementR, but met with no palreolithic reward.· So the matter stands. Sir A. C. Ramsay, Mr. Bristow, Mr. Whitaker, and others have seen some of the sections described by Mr. Skertchly, and have agreed with him that brickearth said to contain Palreolithic implements is older than the Boulder Clay, and of course such an expression of faith is not difficult. The great desideratum is, and I have no doubt Mr. Skertchly would agree with me, that someone else should be fortunate enough to find some unquestionable Palreolithic implements in situ beneath a clear and definite accumulation of the Boulder Clay. I thought it was desirable to make this statement, although it adds nothing to the information respecting the beds. At Norwich there is a considerable accumulation of valley-gravel by the Great Eastern Railway Station at Thorpe, bnt this has yielded no Palreolithic implements and no remains of the
* 'Proc. Norwich Oeo1. Soc,,'
Vol i, p.62.
t ' Geology of the Country around Norwich,' p. 110.
GLdCIAL DRIFTS OF NORFOLK.
127
lIfammalia usually found in association with these ancient works of man. Indeed, the implements that have been found in the rivergravels of East Norfolk are of Neolithic type; the few Palreolithic implements recorded from this part of the county having been picked up on the surface of the ground.* On the coast, however, near West Runton, an implement was found by lIfr. A. C. Savin, in old valley-gravel. Further west I obtained information respecting the discovel'y of a large Palreolithic implement in the gravel at Wells. Remains of the Mammoth were also obtained, which I saw. Unfortunately the implement was not forthcoming j however, there could be little doubt that it was found, for my informants were two Doctors at Wells, who happened to agree upon the point. t I will not, however, draw any conclusion from the possible occurrence of this implement; but the finning Mammoth remains is equally significant in a geological point of view, and no doubt this gravel is of much about the same age as that which yielded the Palreolithic implement at Runton. The formation of the marshes north of Wells is, perhaps, connected with this subject. They appear to be relics of an old valley, in fact the alluvium of a valley which at one time was bordered on the north by hills that have been destroyed through the encroachments of the sea.t The older elephant- and implement-bearing gravels of Wells and Runton may, perhaps, be remnants of the early gravels of the river which flowed along this valley. Possibly it was connected with the Ouse which we know, at Bedford and other places, contains ancient valley deposits with Palreolithic implements and Pleistocene Mammalian remains. These suggestions might be extended further, in connection with the numerous Pleistocene organic remains dredged up in the North Sea, and more particularly off the Dogger Bank, a shoal under 10 fathoms, and about 120 miles N.N .E. of Cromer. From this bank many Mammalian remains have been dredged which belong
* 'Geology of the Country around Norwich,' p. 145; 'Geology of the Country around Diss,' &c., by "F. J. Bennett, p. 19. t ' Geology of Fakenham,' &c. p.36. t In a paper on 'The Scenery of Norfolk' (" Trans. Norfolk Nat. Soc.," Vol. iii, p. 453). I attributed to my colleague, Mr. Reid, this suggestion about the origin of the salt-marshes. He informs me this was a mistake, wherefore I now take the burden of the opinion upon myself,
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FlO. I.-Diagrammatic Section to illustrate the mode of occurrence of the Glacial Drifts in Norfolk and part of Suffolk. The length of the cliff.section from Happisburgh to Weybourn is about 20 miles, and the distance inland from Weybourn to Fakenbam is about 14 miles. Between Carton and Happisburgh there is a gap of abont 20 miles; the portion of the cliff shown at Carton represents about 5 miles. The vertical scale is exaggerated, and the geological details are generalized.
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GLACIAL DRIFTS OF NORFOLK.
129
to the group that characterises the old Thames-Valley deposits of Ilford and other places. * When the Thames united its waters with thoRe of the Rhine, and flowed over what is now the bed of the North Sea, the Ouse may also have been a tributary, and this old bank called the Dogger may be a relic of the period. The Thames-Valley Deposits are no doubt later than the Chalky Boulder Clay, and are considered Post-Glacial in the sense of being newer than the latest glacial deposits of the district; but they are Inter-glacial if we include in the Glacial Epoch the later evidences of ice-action in North Britain.
ORDINARY
MEETING.
FRIDAY, MAY 1ST, 1885.
W. TOPLEY, Esq., F.G.S., Assoc. Inst. C.E., President, m the Chair. The donations to the Library since the previous meeting were announced, and the thanks of the Association were accorded to the donors. The following were elected members of the Association:Richard Butler j Percy E. Newberry; and George Wilks. A Special General Meeting to consider proposed alterations in the Rules was announced. The following paper was then read : , On Wingless Birds, recent and fossil, and on Birds a8 a Class,' by Dr. Henry Woodward, F.R.S., F.G.S. (Publication of this paper is deferred.)
* See papers by W. Davies, 'Geol. Mag.,' Dec. II, Vol. v, pp. 97,443,
111
would fall from a cliff. In that case it would rest upon the pebbles at the base of the cliff, and although much of the mass would be either ground down into pebbles or washed away, its nucleus would be occasionally preserved unmodified, and surrounded on all sides by the well-rounded pebble-beds. THE GLACIAL DRIFTS OF NORFOLK. By HORACE B. WOODWARD, F.G.S., of the Geological Survey of England. The subject of the Glacial Drifts, unfortunately, is by no means adapted for ready writing nor calculated to excite great enthusiasm j for the subdivisions of the beds are a fertile source of discussion, and there is no agreement whatever about their method of formation. The Drifts do not" behave" like other and older formations, for although they may occur regularly for a few miles-Boulder Clay over Sand or Gravel-on the borders of a valley, yet all at once the Clay plunges to the lowest level of the ground, in defiance of geological rules. You may find a Clay-pit in one field and a deep gravel-pit in the next, and this without the change we are taught to expect in the form of the ground; and, sometimes, where the pits are but few yards apart, it may be difficult to determine the newer deposit. The ordinary tests for identifying or distinguishing strata furnish little help to the student of the Norfolk Drifts. The fossils found in them are either certainly derived, or more or less fragmentary and probably derived. The lithological characters of the strata are variable, while the same general characters are repeated in successive accumulations, so that local peculiarities can be taken as guides only by those who work gradually over a district from pit to pit. Even stratigraphical succession affords no sure means of identification, for lenticular beds of sand or gravel occur in both Upper and Lower Boulder Clay; and the evidence of erratic blocks, although useful, is no infallible clue, as one may often search the Boulder Clay in vain for other stones than Chalk and flint. After spending about a year in Norfolk I began to believe I knew all about the Drifts, but during the following seven years of my sojourn in that county, as I moved from place to place, I somehow seemed to know less and less; and I cannot say what would
112
H. B. WOODWARD ON
'rH~
have been the result, but fortunately the Geological Survey of tbe county came to an end. While in Norfolk, I was more than once asked to give such a description of the Glacial bcds, that from it anyone could go into the field and recognize the several divisions. Tbis is a request with which I never felt able to comply. Distance, however, lends enchantment to the view, anu if I strive to give my notions of these Drifts, now that I am :\way from their perplexing details, perhaps my remarks may possess more value than if they were written on the spot. Two questions come before us. What is the broad general grouping of the beds? Wl!at is the story they tell? If I succeed in answering these questions, and in extracting some hnrmony from the accompanying sections, my task lllay not be in vain; and although I do not wish to neglect the opinions of others, I need not attempt a statemen"t of all the conflicting views on Norfolk Drifts which a study of the literature woulu supply; for such a proceeding would extend my paper to undue length, and the result woulu he simply bewiluering. Broadly speaking the Drifts admit of two divisions, each of which locally contains many kinds of marl, clay, loam, sand, and gravel. The Lower division (or Lower Glacial) is well shown in the cliffs between \,yeyhoQrn and Happisburgh. It comprises the Cromer Till, and the Contorted Drift with interbedded and over~ lying (Middle Glacial) sands and gravels. These beds form the main mass of the celebrated" mud cliffs" of Norfolk. The Cromer Till is a tough bluisb"grey unstratified Boulder Clay, containing fragments of l'ellina Balthica, .Jlya arenaria, Cardium edule, and Cyprina Tslandica. It contains also many glaciated fragments of Chalk and flint, of septaria (probably from tbe Kimeridge Clay), and Carboniferous Limestone; as well as many igneous and metamorpbic rocks, such as mica-schist, granite, felstone, basalt, &c. In tbis Till fine examples of glaciated stones are more abundanttban in any otber Drift in Norfolk. Overlying tbe Till come thick beds of brown loam, chalky clay, gravel, and sand, which in many places are so twisted and di~ t.ubed, that tbe name Contorted Drift was applied to them. It is in fact a conglomeration of all kinds of sediments, although loam and marl preuominatc. Among the remarkable features of this
GLACIAL DRIFTS OF NORFOLK.
113
Contorted Drift are the large boulders which it contains, not merely those of quartzite, grit, gneiss, granite, and basalt, of which blocks measuring over 6 feet in length have sometimes been found; but huge boulders of Chalk-with-flints, one re-deposited mass 01' rather strip of which is upwards of 180 yards in length. Above the Contorted Drift come the sands and gravels ca11ed " Middle GlaciaL" The sands in places contain what may be termed shoals of broken shells, and these, more conspicuous in the cliffs of Gorleston and Cortou, between Yarmouth and Lowestoft, were noticed by the earlier geologists as re-deposited Crag sheUs. By searching the cliffs and sifting loads of the material, sent' home to them in sacks, Messrs. Wood and Harmer were enabled to give a list of over 100 species'*' of mo11usca from these sands. The assemblage is a very curious one. With the exception of one Venus, a LOI'l}II'S, and some new species, a11 the shells are found in our Crag deposits; and it is very natural to suppose that they were derived from them; but while coutaining a number of species which might have come out of the Corallinc Crag, and others that might have been derived from the Red and Norwich Crags, yct" not a trace or fragment of most of the common strong sheUs of the Coralline and Red Crags has occurred." Nearly aU the specimens found, it is true, are more or less rolled, but fragile shells like Anomia ephippium are occasionally preserved. Messrs. Wood and Harmer conclude that the fauna was contemporaneous, although the she11s bear evidence of having been shifted and rolled by currents which brought them from some other part of the seabottom; while in their opinion some of the delicate shells may have been transported by floating masses such as seaweed. These conclusions I believe first started the notion of Interglacial mild periods-for the presence of Coralline Crag forms suggested that somc connection with the Mediterranean area had been reopened by submergence of the land at this period. Mr. Clement Reid, who has carefully examined the sheUs found in the Glacial sands of the Cromer Cliffs, remarks :-" There has been much discussion as to the contemporaneous or derivative origin of the 'Middle Glacial' fauna, and it is interesting to trace in a new district the same peculiarities in the fossils which led Mr. S. V. Wood to consider the fauna to be contemporaneous with the deposit. It is not improbable that a large proportion of the fragments of the 'I<
See 'Supplements to the Crag Mollusca.'-Palmontograph. Soc.
114
H. B. WOODWARD ON THE
common shells may be derivative; but near Cromer, as at Yarmouth, the peculiar and characteristic types are the most perfect. Though the commonest forms are Tellina Balthica, Cardium edule, Cyprina Islandica, and Mya a/'enaria, of the last three nothing but small fragments were seen, and of Tellina Balthica only a few nearly perfect valves; but the single specimens of Nassa reticosa, Anomia, and Dentalium w"ere nearly perfect, as were two or three of Scalm'ia G1'GJnlandica and Natica Grceniandica? The re-appearance of Crag forms may be explained by the submergence of the land to a greater extent than had occurred since the time of the Coralline Crag, thus re-opening the connection with the southern seas, and allowing species long exterminated in this area to again migrate into it." * I dwell at some length on this subject, because it is a very important one, and because I have for some time felt great doubt about the shell fauna being contemporaneous. Of course the aspect of thp, beds alone makes one sceptical, and it is admitted that the shells did not live on the spots where they have been accumulated. It may be remarked that, traced southwards, these so-called Middle Glacial Sands pass mostly into gravels. which underlie the Chalky Bonlder Clay over a considerable part of Essex, and that only in two or three places in Suffolk, sonth of Corton, have fragments of Crag shells been found in the Drift of this portion of the eastern counties. Moreover, near Hertford and other places, seams of Boulder Clay have been met with in gravel beneath the main mass of Chalky Boulder Clay-which gravel has been grouped as Middle Glacial by Mr. Wood himself, t and this does not support the view of a much milder climate. Regarding the shells as mainly derived from the Crag deposits, the question arises where are (or where were) the beds whence the shells were obtained? For the Coralline and Red Crags are exposed only to the south of the tracts, where we meet with these fossiliferous Glacial sands. In 1860 Mr. T. F. Jamieson described some beds of sand and gravel on the eastern border of AberJeenshire, which contained fragments of shells, belonging to Crag species. At that time he
* . Geology of the Coun try around Cromer' (' Geol. Survey'), pp. 93, 94. t See' Guide to the Geology of London.' By W. Whitaker. 4th Edition, 1884, p. 62.
GLACIAL DRIFTS OF NORFOLK.
115
thought that some part, at least, of the gravel itself, might be a Preglacial deposit of Crag age. Three years ago, however, Mr. Jamieson brought forward further information respecting these deposits. He had ascertained that what appears to be a Glacial bed underlies them, and he now believes that in their present state these accumnlations are all of more recent origin than their fossil contents would indicate. * However, the important part of the subject is that the shell fragments comprise forms found in the Coralline, Red, and Norwich Crags, as well as in more recent deposits, although all of the species, excepting Tellina Balthica, occur in the Red Crag. The absence of Tellina obliqlta, so common in our Norwich and Red Crags, is noteworthy j but the occurrence in Aberdeenshire of C!JjJl'ina 1'Ustica, large forms of Pectunculus glycimel'is, of Venus casina, and of Voluta Lambe1·ti, strongly suggest their derivation in part from deposits of the age of the Coralline Crag, and this is Mr. Jamieson's opinion. I mention these facts to show that Oldel' Pliocene, as well as Newer Pliocene accumulations, took place so far north as Aberdeenshire; and hence all difficulty is removed in seeking a northern derivation for the shell accumulations in the so-called "Middle Glacial" Sands of East Anglia. Moreover, local geographical distribution of the mollusca in the Crag pcriod may account for the peculiarities in the fauna. The so-called Middle Glacial Sands are intimately connected with the Contorted Drift; their gravelly equivalents in the south do not indicate deeper water conditions, nor have we any southerly fossiliferolls beds of this age, which we might expect had the fauna migrated in Interglacial times from the Mediterranean area. Hence, we are justified in regarding the question, at any rate, as an open one, and in ma1dng the suggestion that the Middle Glacial Shells may have been largely derived from old Crag accumulations, now entirely destroyed or buried up beneath the waters of the North Sea. It is right to mention that Messrs. Wood and Harmer have expressed their opinion that the Contorted Drift was overlaid unconformably by these Middle Glacial Sands and Gravels, and that during the interval between them the valley system of East Anglia was marked out. This is not borne out by the evidence furnished in the coast-sections, for, as Mr. Reid has shown, the
* . Qnart. Jonrn. Geol. Soc.,' Vol. xxxviii, p. 145.
116
H. B. WOODWARD ON rHm
basin-shaped hollows in which the sands and gravels frequently lie, are due to contortion, and not to erosion. Where anything like unconformity exists, it is where these gravels and sands have been rearranged, and such appears to be the case near Blakeney, in Norfolk, where these reconstructed gravels have assumed the form of Eskers. They are probably of later Glacial age, and may perhaps be grouped with the Cannon-shot gravels to be mentioned presently. Mr. T. V. Holmes has described the peculiarities of these Eskers. '*' We thus have in the Cromer Cliffs evidence in descending order of sand and gravel, loamy beds (Contorted Drift, &c.), and Till or Lower Boulder Clay. This order is maintained over a good part of north-east Norfolk; and as the loamy beds are prevalent in the low grounds, and the sands and gravels overlying them form the hills, the geology seems fairly simple. The Geological Survey Map, indeed, shows the general strncture, gravel and sand (coloured pink) resting on loam or brickearth (coloured yellow). Passing westwacds the loam contains huge masses or jambs (as they are called) of marl or chalky clay, and these, where sufficiently prominent and extensive, are marked on the map with the same tint as Upper or Chalky Boulder Clay (blue). Still further west the main mass of the Drift bcneath the sand and gravel is chalky or marly; consequently the map is to a very large extent coloured blue, with patches only of yellow, where brickearth or loam is developed. The real fact of the case is, that the Lower Glacial Clays, which, east of Cromer and near Norwich, consist chiefly of brown stony loam, become westwards so like the Chalky Boulder Clay, that no one, from the evidence of pit sections, could tell one from the other. As a rule, the Lower Glacial Drifts rest on a very even surface of the Forest Bed Series, which consists of sands, gravels, and laminated clays. Mr. Reid mentions, however, that in places where the Till rests on laminated clays, the beds have been slightly crumpled. The Cromer Till may be regarded as the product of an ice-sheet, deriving its shell-fragments from the bed of tIle sea or from preglacial deposits over which the material was pushed. Submergence
* 'Proc. Norwich Geol. Soc.,' Vol. i, p. 263, and' Geol. Mag.,' Decade II. Vol. x, p. 438. See also' Geology of the Country around Fakenham,' &c, (' Geol. Survey'), p. 35.
GLACIAL DRIFTS OF NORFOLK.
117
following, the succeeding Contorted Drift, which exhibits evidence of stratification and sometimes of ripple-marks, was probably deposited in the sea; while some of the large blocks of igneous and metamorphic rocks may have been brought by ice-bergs, perhaps from the Scandinavian area. Sands and gravel£; succeeded the more muddy sediments, and these deposits were subsequently acted upon by a force sufficient to produce the violent contortions before mentioned; but before attempting to explain these contortions we must turn to the next deposit. Spreading over a great part of South Norfolk, and over much of Suffolk, extending to the northern margin of the Thames Valley near Brentwood and Epping, and well known, too, at Finchley, is an accumulation of more or less chalky clay, clay containing groundup chalk and chalk stones in abundance, together with flints, and flint pebbles, and also a variety of rocks and derived fossils. Of these, Oolitic material is conspicuous, and the great clay formations, like the Lias, the Oxford Clay, and the Kimeridge Clay, appeal' to have suffered more in the formation of this Boulder Clay than the Oolitic limestones which usually intervene between them. Among the fossils we find Gryph(fJa inc'Ul'va, .wyacites, Gryph(fJa dilatata, and Belemnites abbreviatus. The character of this deposit is fairly uniform over a large area, but while spread out in extensive sheets over the higher grounds of South Norfolk, Suffolk, and Essex, it l'ests now on sand, sometimes on loam, and occasionally on the Norwich Crag, and often it descends to the bottom of the valleys on a level with the Alluvium. The distribution of this Upper 01' Chalky Boulder Clay in Norfolk is very remarkable. One sheet of the Geological Survey Map south of Norwich (66 S.E.), is nearly covcred with it, whereas the sbeet to the north (66 N.E.) is mostly covered with the loam called Contorted Drift, and classed with the Lower Glacial. A glance at the two maps naturally suggests that the two accumulations are varieties of one Boulder Clay, and I may say I have at times held to this view; for over the greater part of the area where the Chalky Clay is developed, there is very little of the Lower Boulder Clay beneath it. The sequence of Upper, Middle and Lower Glacial is the exception and not the rule. We have, it is true, the section at Corton, where Joshua Trimmer, first pointed to the evidence of an Upper and Lower Boulder Clay, but here the Lower Boulder Clay is a very feeble and irregular ac-
118
H.
n.
WOODWARD ON THE
cumulation compared with the Lower Glacial Clays at Happisburgh and Cromer; and it is open to question whether the brown stony loam there represents the Cromer Till or a portion of the Contorted Drift; but from the character of the Boulders noted by my colleague, Mr. J. H. Blake, in the Corton Lower Boulder Clay, I should regard it as belonging to the Contorted Drift.'" In this case the Cromer Till is only a very local deposit, and Mr. Reid does not even identify it at Cromer. We may build up ollr sequence, however, by passing from Corton to Happisburgh, regarding (as Messrs. Wood and Harmer have done) the sands on top of the Cromer Cliffs as the same as those at Corton j but, to say the least of it, it is unfortunate that we have no evidence anywhere along the Cromer Cliffs of the Upper or Chalky Boulder Clay. Inland there are a few pit-sections which show the sequence of Chalky Boulder Clay, sand, and stony loam or Lower Boulder Clay; but most of these sections show in the same pit the sand tapering away, and then the two Boulder Clays come together, and their separation is not a happy task. Fortunately in East Norfolk the Lower Clay maintains its character of a brown stony loam, so that whenever a section is exposed, it may usually be distinguished from the more chalky Upper Boulder Clay in that area. It was my duty to map a considerable portion of West Norfolk around Fakenham and Wells, and I had to join up from this area with another tract I had surveyed to the east around Aylsham and North Walsham. At Fakenham I commenced mapping Boulder Clay which presented all the characteristics ofthe Chalky Boulder Clay, and as I Havelled eastwards it appeared to merge into the formation I had there grollped with the Contorted Drift. I could not help it, although I felt sorely grieved and perplexed. The mere separation of clay or marl from sand and gravel was not in itself a very troublesome process, but to try and discriminate Upper and Middle and Lower Glacial deposits taxed my equanimity to the utmost. When the mapping was accomplished the map looked so simple, a foundation of clay with patches of gravel and sand on i~, that no one could sympathize with my many anxieties and doubts; but when I came to write the description, then, as your President re-
* See Sheet 128, 'Horizontal Sections'
(' Geol. Survey').
GLACIAL DRIFTS OF NORFOLK.
119
marked, and justly too, the explanation seemed far more complicated than the map it was intended to elucidate! "" If you glance at the Cromer map, you can judge how little the surface geology, as there depicted, tells of the great contortions which are so conspicuous in the cliffs. My case was similar. Nearly every good section showed that the beds were very much disturbed. Many railway-cuttings have been made (more to the interest of geologists, I fear, than to the shareholders in the companies) and these cuttings almost invariably displayed the irregularities of the strata; so that I frequently felt that the cuttings added to, rather than diminished, the difficulties of mapping, for they showed how impossible it was to be minutely accurate. For instance, on comparatively low ground, where the general surface evidence indicated clay, and the bordering hills were clearly sand and gravel, with a marked feature, the cuttings would show not merely loam and marl and boulder clay jumbled up together, but large included beds of sand and gravel. Hence a sand or gravel-pit might be opened in the midst of a tract marked as clay on the map, when of the existence of such material there would be no surface evidence. Consequently any written explanation of the district must naturally make the geology seem much more complicated, as it really is, than it appears to be on the map. However, I frequently sought comfort in the Cromer Cliffs, feeling that the contemplation of such a contorted, tumbled, higg-Iedy-piggledy arrangement of beds was enough to confound any field-geologist who wonld attempt to map out the strata t in great detail. It is told of Dr. Buckland that, when travelling in the Eastern Counties, he knew when he was on the Boulder Clay by the rosy cheeks of the lasses; but that I fear would be evidence on which the geological surveyor could not wisely rely, if it be not a libel on other subsoils. My chief difficulty, in reality, arose from trying to separate the Upper Chalky Boulder Clay from the Lower Boulder Clay, which in West Norfolk becomes as a rule more chalky than the bed above; and in the end I had to give up attempting to draw a line, which could not be defined with any approach to accuracy. The difficulty in colouring the maps was obviated by commencing to colonr blue the marl masses which occur in the loamy Conto~ted Drift, and
* See t
'Geology of the Country around Fakenham,' &0. See Sheet 127, 'Horizontal Sections' (I Geol. Survey'), by C. Reid.
120
H. B. WOODWARD ON THE
when the marl predominated colouring the whole of it blue, like the Chalky Boulder Clay. Although the term Contorted Drift is usually confined to the Lower Glacial Beds, yet similar contortions also affect the Chalk and sometimes the Norwich Crag. On the Cromer coast we find that the oontortions decrease in intensity as we proceed in an easterly direction j for while at Sherringham and Cromer the disturbances are violent in the extreme, at Happisburgh the beds are little if at all disturbed. The conclusion to which Mr. Reid and myself came, was that the contortions were produced by the agent which formed the Chalky Boulder Clay, and this view was, I believe, first suggested by Mr. S. B. J. Skertchly. Sometimes this Boulder Clay rests on a substratum that shows little or no disturbance. The cliff-sections at Kessingland and Corton, in Suffolk, furnish examples. The clay rests on sand, and As is the rule with such the junction is well-marked all along. junctions, the lower part of the Boulder Clay is sandy, and the line of division, though sometimes undulating, is distinct. Where the Boulder Clay rests on clay, the same distinct line may also be observed; but almost invariably where the underlying clay contains streaks or nests of sand, these are very much contorted. The fact is that the clay without these nests of sand would not well exhibit the contortions j while where sand alone is seen under the Boulder Clay, contortions may be absent because the deposit was of too yielding a nature to be acted upon. In one or two localities where marked lines of bedding occur in the sand, I have, however, found evidencl's of disturbance. On the whole, my experience is that the beds beneath the Boulder Clay of Norfolk are more frequently contorted than not, and that the agent which formed the Chalky Boulder Clay. was instrumental in disturbing the strata over ·which this clay was accumulated. This is an assertion which I do not think anyone acquainted with the country would dispute. What the agent was is another matter, and there, unfortunately, the principal observers agree to differ. In studying the junctions of Boulder Clay with various deposits on which it rests, we sometimes find, as in W est Norfolk, that on the Chalk the line of demarcation is most obscure. It is difficult to say where the Chalk ends and the Boulder Clay begins. In
121
GLACIAL DRIFTS OF NORFOLK.
these cases it appears evident that the Glacial Drift was formed chiefly from the Ohalk of the district. In this way we may account for some of the very marly varieties of the Boulder Olay, which in places are little else than ground-up Ohalk. Analysis of one of these chalky drifts, blunt for lime near Holt, showed 91 per cent. of carbonate of lime, and the Rev. O. Fisher has spoken of such drift as "an ancient manufacture of ' whiting' on a magnificent scale."* Mr. Reid observes that "The masses of reconstructed Ohalk so common in the Contorted Drift are probably nothing but a later stage of the transported boulders, in this case so shattered and mixed with clay that they form a sort of transition to an ordinary Boulder Olay. From the very marly character of the Oontorted Drift when traced westward, it seems not improbable that that portion of the deposit is continuous with, and passes laterally into, the Great Ohalky Boulder Olay. The general structure of Norfolk and Suffolk appears to show that the whole of tbe contortions are of one age, that of the greatcst glaciation, or of the Great Ohalky Boulder Olay, and it is probably to this period that the disturbances on tbe coast may be referred." t These remarks furnish a comforting explanation of the difficulties met with in thc country around Fakenham. There, where the later Boulder Olay passed directly over the clayey Lower Glacial beds, it no doubt became incorporated with them, causing one contorted mass, and we cannot separate the two deposits. In other places we find the flint-layers of tbe Ohalk disturbed, as if that rock had offered a local impediment, perhaps a low hill or cliff against which the icy agent impinged. Mr. Reid bas explained the flexures in tbe Ohalk at Trimingham as due to glacial action in the form of an ice-sheet. Mr. S. V. Wood previously caUed attention to disturbances in tbe Obalk at Litcham, which he attributed to tbe passage of a glacier over the surface of the rock; and when the Geologists' Association came to Norwich tbe members visited a pit at Trowse, where I pointed out the Ohal k uptilted and underlaid by Boulder Drift; so that tbe disturbance was evidently due to glacial agency. I have since described some sections near 'Veils, where the Ohalk is .. See ' Geology of Fakenham,' &0., p. 23. t ' Geology of the Country around Cromer,' pp. 115-117.
VOL. IX., No.3.
10
122
H. B. WOODWARD ON TIlE
similarly disturbed in connection with the Glacial Drift.- These disturbances of the Chalk help us to explain how the huge isolated masses, or "boulders," of the rock may have been formed. The occurrence of such large shifted rocks in Drift is not confined to Norfolk, for there is an immense mass of detached Chalk in the well-known pit called Roslyn Hole, near Ely, and great boulders of Inferior Oolite and Marlstone occur in the Drift of Lincolnshire. In West Norfolk too there is one celebrated stone called the Merton Boulder, which measures nearly 12 feet in length, with a thickness and breadth of about four or five feet. The derivation of this rock was long a puzzle to Norfolk geologists, until Mr. Whitaker identified it as a Neocomian sandstone of local deriva. tion·t No doubt the Chalk at Trimingham furnishes the most striking evidence of the formation of these huge boulders. Mr. Reid remarks: "If the ice-sheet, instead of flowing over the beds, happens to plough into 01' abut against them, it would bend up a boss of Chalk, as at Beeston. A more extensive disturbance, like that at Trimingham, drives before it a long ridge of the beds, and nips up the Chalk till, like a cloth creased by the sliding of a heavy book, it is folded into an inverted anticlinal. A slight increase of pressure, and the third stage is reached-the top of the anticlinal being entirely sheared off, the Chalk boulder driven up an incline, and forced into the overlying Boulder Clays."t With this view I coincide. It will not, however, be imagined that this is the only explanation that has been given of the phenomena, for when there is room for diversity of opinion geologists fully avail themselves of it. Icebergs have been considered as the agents for transporting the boulders; and Mr. Mellard Reade believes that they were severed from old cliffs by the expansive force of ice in fissures, and then shifted by coast-ice. § I cannot, however, attempt to discuss the various explanations that have been given of the formation of our Glacial Drifts. The agents concerned in their formation may be land-ice, coast-ice, and icebergs; and it is not always possible to '" 'Proc. Geol. Assoc.,' Vol. v, p. 513; 'Geology of Country around Norwich,' p. 135; • Geology of Country a"ound Fakenham,' pp. 9, 2-1. t • Geology of Country around Attleborough,' &c., by F. J. Bennett, p.10. t 'Geology of ·the Country around Cromer,' p. 115. § • Quart. Journ. Geol. Soc.', Vol. xxxviii, p. :122.
GLACIAL DRIFTS OF NORFOLK.
123
localize their action. Unfortunately, we have very little information concerning what kinds of accnmulations are being formed by landice in the arctic regions. There the icy agents can be studied; but the effects are not, as a rule, so conspicuons. In Norfolk we see the results, and have to infer what were the agents. In the formation of our Chalky Boulder Clay, however, icebergs are generally admitted to have had little or no influence, for the ice from which the floating masses would be severed must have passed over considerable tracts of Chalk, and the Chalk would have been submerged if the icebergs were to have fair play. Mr. Wood advocated the view that the Chalky Boulder Clay was extruded at the foot of an ice-sheet that enveloped the Yorkshire and Lincolnshire Wolds; but the general absence of stratification goes against the view of this clay having been for the most part deposited under water. We require, too, an agent capable of exerting a comparatively uniform influence over wide tracts, of abrading and pushing on material in a manner more extensive than could be attributed to coast-ice, althongh this view of its formation has met with a warm advocate in Mr. Jukes-Browne. Moreover, the Clay has been much compressed, and is so tough and hard in places that navvies engaged in making railway-cuttings have told me they never had a more troublesome material to deal with. The occurrence of the chalk lumps in the clay may perhaps be accounted for in the following way. The surface of the Chalk in Norfolk, along the sea-margin, and in places inland, is seen to have weathered in a very rubbly form, to a depth sometimes of six or eight feet. Frost and rains have no doubt been the chief influences in producing this; and this weathered Chalk would furnish " ready made" the very material for the Chalky Boulder Clay, which consists so largely of lumps of Chalk which have not necessarily been rounded by rolling. Mr. F. J. Bennett, too, has suggested that much of the material of which Boulder Clay was formed may have been the soils or subaerial debris on the surfaces of the land over which the ice passed. This is a subject well deserving of careful study, and it has been discussed in some of the publications of the United States Geological Survey. II II 'Proc. Norwich Geol. Soo.,' Vol. i, p. 256. Geology,' ed. 2, pp. 325, 894.
See also A. Geikie, 'Text of
124
If. R. WOODWARD ON THE
One other depol>it must be mentioned. Scattered over the high grounds of Holt and Cromer, and resting on the Chalky Boulder Clay in many places in W est Norfolk, and near Norwich, are great accumulations of coarse boulder gravel-gravel containing large blocks of flint and even paramoudras, all more or less rolled and knocked about. Some few igneous rocIrs occur also, as well lis pebbles of quartz and quartzite. To these deposit.s the name Cannon-shot gravel was applied by Mr. Wood, because the majority of the stones in some places are lC rolled into the shape and dimensions of the now obsolete cannon"hot of from 121bs. to 321bs. calibre." The deposit seems to be intimately connected with the Chalky Boulder Clay, and Messrs. 'Vool! and Harmer have attributed the origin of these gravels to some local modification of this deposit by powerful currents. It is, indeed, an ~ecnmulation that bears eviLIenee of having been formed in a tumultuous way, but the Chalky Clay itself does not yield such large flint boulders in abundance. The question is, whence came the flints-for the deposit is not often found directly on the Chalk, otherwise we might account for it by ordinary marine action 011 a foreshore of that formation. I have ventured to suggest that during later Eocene and Miocene times accumulations of flints might have been formed by subaerial action on the Chalk surfaces of West Norfolk, and that in Glacial times they furnished material for the gravels. * In West Norfolk, where the Chalk bills are covered by straggling outliers of Boulder Clay and gravel, the Lower Drifts are probably not represented. The conclusion that might be drawn from these remarks is that, after all, the divisions of the Drift possess little more than local value. It might also be concluded that, while the work on the Geological Survey is generally considered to be olle of the most delightful of occupations (by those who have had no experience of it), yet to be engaged in NorfoUr trying to distinguish and separate gravels and Boulder Clays, and to say whether there is Uppel' and Middle and Lower Glacial, and, if so, which is whicb,-often while a keen east wind is blowing-is not an enviable situation, and enthusiasm may then langui8h. Olle is sometimes tempted to exclaim that anyone who wished to bave a clear and definite notion of the succession of Norfolk Drifts should confine his attention to certain sections. If he
* 'Trans. Norfolk Nat. Soc.', Vol
iii, pp. 444, 447.
GLACIAL DRIFTS OF NORFOLK.
125
wished to feel confident of the triple division, one series of sections should be visited; if a twofold division would better agree with his notions, other sections might be selected, and so on. My own opinion respecting the Drifts has fluctnated, according to different districts which I have been called upon to examine; and yet probably no district furnishes better sections of the Glacial Drifts than are to be found in Norfolk. Looking at the beds, as we have tried to do, in a general way, we discern that two great divisions may be recognized-the Cromer Till and Contorted Drift, gronped together as Lower Boulder Clay, followed by sands and gravels; and the Chalky or Upper Boulder Clay, with associated sands and gravels. The Lower Boulder Clay, as Mr. John Gunn has remarked, is characterized by boulders of an igneous type, and it often contains Pleistocene shell-fragments. It may have been derived from the Ilorth and north-east. The Upper Boulder Clay is characterized by .Jurassic detritus, and was probably derived from the north-west. But the most important distinction, perhaps, is in the disturbances to which the Lower Glacial Beds have been subjected by the agent which formed the Chalky Boulder Clay. Anyone who wishes for details may consult the Geological Survey Memoirs on portions of Norfolk, in which most of the sections are described, and in which as much detail will be found as the most ardent geologist could desire j while those who wish to study the theoretical questions connected with the Drifts will find ample material in the Inany papers by Messrs. Wood and Harmer. '" It is only right to say that their admirable geological map of the Crag district is in all essential particulars substantiated by the more detailed lllap of the Geological Survey.t Turning now to another subject, the occurrence of Palreolithic implements is a topic that cannot be neglected in any account of the Glacial Drifts of Norfolk. Some years ago now-it Was in 1876-Ml'. S. B. J. Skertchly announced his discovery of flint-implements beneath the Boulder Clay of East Anglia.t I do not wish to enter into all the parti-
* For a Bibliography of Norfolk Geology, Bee the Geological Survey , Memoir on the Country arouud Norwich.' t See' Supplement to the Crag Mollusca' Part i. 1872. ::: ' Geol. :Mag' Dec. IL, Vol. iii, p. 476; see also 'Manufacture of GunHints' (' Geol. Survey'), p. 65; and Prof. J. Geikie's 'Great lee Age,' Ed. 2, p. 565.
126
H. B. WOODWARD ON THE
cuI aI'S of this announcement. Unfortunately the evidence upon which Mr. Skertchly based his conclusions has not been published in detail, and they therefore cannot be tested and verified in the way in which it is desirable that all discoveries shonld be treated; but, after seeing many of the sections with him, I had occasion to deliver an address before the Norwich Geological Society, and then stated that" The interval between the Upper and the Middle and Lower Glacial Beds is probably marked by the Brandon Beds, which Mr. Skertchly has shown to contain our earliest records of man's existence in this country."· The story of my conversion is briefly this: The first time I went, I saw certain sections, and came away unconvinced, nay sceptical. On the second occasion, I saw other sections, and one in particular at a brickyard near Mildenhall. Here there was brickearth, clearly overlaid by Boulder Clay,' and Mr. Skertchly informed me that Palreolithic implements had been fonnd in this brickearth. It is true I found no implements, nor did he find one while I was there; but there was no escape from the co"nclusion that the brickearth was older than the Boulder Clay. This bed of brickearth, and other beds of brickearth near Thetford, interested me much, for I had come across similar beds near Norwich, which were older than the Boulder Clay. These I diligently searched for flint-implementR, but met with no palreolithic reward.· So the matter stands. Sir A. C. Ramsay, Mr. Bristow, Mr. Whitaker, and others have seen some of the sections described by Mr. Skertchly, and have agreed with him that brickearth said to contain Palreolithic implements is older than the Boulder Clay, and of course such an expression of faith is not difficult. The great desideratum is, and I have no doubt Mr. Skertchly would agree with me, that someone else should be fortunate enough to find some unquestionable Palreolithic implements in situ beneath a clear and definite accumulation of the Boulder Clay. I thought it was desirable to make this statement, although it adds nothing to the information respecting the beds. At Norwich there is a considerable accumulation of valley-gravel by the Great Eastern Railway Station at Thorpe, bnt this has yielded no Palreolithic implements and no remains of the
* 'Proc. Norwich Oeo1. Soc,,'
Vol i, p.62.
t ' Geology of the Country around Norwich,' p. 110.
GLdCIAL DRIFTS OF NORFOLK.
127
lIfammalia usually found in association with these ancient works of man. Indeed, the implements that have been found in the rivergravels of East Norfolk are of Neolithic type; the few Palreolithic implements recorded from this part of the county having been picked up on the surface of the ground.* On the coast, however, near West Runton, an implement was found by lIfr. A. C. Savin, in old valley-gravel. Further west I obtained information respecting the discovel'y of a large Palreolithic implement in the gravel at Wells. Remains of the Mammoth were also obtained, which I saw. Unfortunately the implement was not forthcoming j however, there could be little doubt that it was found, for my informants were two Doctors at Wells, who happened to agree upon the point. t I will not, however, draw any conclusion from the possible occurrence of this implement; but the finning Mammoth remains is equally significant in a geological point of view, and no doubt this gravel is of much about the same age as that which yielded the Palreolithic implement at Runton. The formation of the marshes north of Wells is, perhaps, connected with this subject. They appear to be relics of an old valley, in fact the alluvium of a valley which at one time was bordered on the north by hills that have been destroyed through the encroachments of the sea.t The older elephant- and implement-bearing gravels of Wells and Runton may, perhaps, be remnants of the early gravels of the river which flowed along this valley. Possibly it was connected with the Ouse which we know, at Bedford and other places, contains ancient valley deposits with Palreolithic implements and Pleistocene Mammalian remains. These suggestions might be extended further, in connection with the numerous Pleistocene organic remains dredged up in the North Sea, and more particularly off the Dogger Bank, a shoal under 10 fathoms, and about 120 miles N.N .E. of Cromer. From this bank many Mammalian remains have been dredged which belong
* 'Geology of the Country around Norwich,' p. 145; 'Geology of the Country around Diss,' &c., by "F. J. Bennett, p. 19. t ' Geology of Fakenham,' &c. p.36. t In a paper on 'The Scenery of Norfolk' (" Trans. Norfolk Nat. Soc.," Vol. iii, p. 453). I attributed to my colleague, Mr. Reid, this suggestion about the origin of the salt-marshes. He informs me this was a mistake, wherefore I now take the burden of the opinion upon myself,
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FlO. I.-Diagrammatic Section to illustrate the mode of occurrence of the Glacial Drifts in Norfolk and part of Suffolk. The length of the cliff.section from Happisburgh to Weybourn is about 20 miles, and the distance inland from Weybourn to Fakenbam is about 14 miles. Between Carton and Happisburgh there is a gap of abont 20 miles; the portion of the cliff shown at Carton represents about 5 miles. The vertical scale is exaggerated, and the geological details are generalized.
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GLACIAL DRIFTS OF NORFOLK.
129
to the group that characterises the old Thames-Valley deposits of Ilford and other places. * When the Thames united its waters with thoRe of the Rhine, and flowed over what is now the bed of the North Sea, the Ouse may also have been a tributary, and this old bank called the Dogger may be a relic of the period. The Thames-Valley Deposits are no doubt later than the Chalky Boulder Clay, and are considered Post-Glacial in the sense of being newer than the latest glacial deposits of the district; but they are Inter-glacial if we include in the Glacial Epoch the later evidences of ice-action in North Britain.
ORDINARY
MEETING.
FRIDAY, MAY 1ST, 1885.
W. TOPLEY, Esq., F.G.S., Assoc. Inst. C.E., President, m the Chair. The donations to the Library since the previous meeting were announced, and the thanks of the Association were accorded to the donors. The following were elected members of the Association:Richard Butler j Percy E. Newberry; and George Wilks. A Special General Meeting to consider proposed alterations in the Rules was announced. The following paper was then read : , On Wingless Birds, recent and fossil, and on Birds a8 a Class,' by Dr. Henry Woodward, F.R.S., F.G.S. (Publication of this paper is deferred.)
* See papers by W. Davies, 'Geol. Mag.,' Dec. II, Vol. v, pp. 97,443,