- Email: [email protected]
Part I. Lower dee-side and the Highland border.
268 PART
1.
LOWER DEE-SIDE AND THE HIGHLAND BORDER. By
GEOR GE B ARROW,
F.G. S.
S EPT EM IlE I{ 12T H .
THE party, which numbered 4 7 in a ll, pro ceeded by train up the Dee Valley to Ba nchory. During the jou rney, attent ion was d rawn to th e great mass es of Glaci al Gravels with which th e lower part of th e Dee Valley was filled. I n th ese, a number of terraces have been cut by streams flowing from the two edges of the local valley glacier that brought down th e gravels; as th e glacier diminished in size the terraces were gradually cut at a lower and lower level. While driving to th e first haltin g place, som e heaps of crystalline limestone by the road-side were pointed out. In many of th ese microscopic crystals of fosterite may be fou nd, perfectl y fresh, as they have been obtained from a quarr y ; in outcrop specimens the mineral is rar ely ide ntifiable. T he first halt was mad e at Beltcraig Farm , a littl e east of th e Fe uch Bridge. It was now explained th at th e da y's work would be divided into two parts; in th e morning it would be shown that th e metamorphic rocks over a large area were penetrated by a vast nu mber of small intru sions of granitic material belonging to a part of the Older Granites (the Cairnshee Granite) . Though often mere threads, they never have chilled margins, but are always granitic ; in some cases th e whole thickness of a small intrusion may be mad e of a singl e crystal of felspar. In the afternoon the margin of one of the Newer Gran ite masses wo uld be examined, and though the mass (the Kincardineshire Grani te) covers an area of over 10 0 square miles, its northeastern edge would be found to possess a fi ne grained a nd q uickly-cooled edge . T here must thu s have been a great cha nge in condition s between th e time of the two intru sion s, repr esent ing a lon g interval of tim e. The metamorphic rocks see n at Beltcraig were stated to belong to th e lowest known portion of th e H ighland series ; being below any that occur alon g the Highland border. They originally consisted of sandy shale, shale and an impure limestone (th e Dee-side limestone) ; these were here altered to gneisses, th e first con taining much felspar and often some sillimanite, th e second containing usually a great quantity of silliman ite in minute need les (fibrolite), while th e th ird was now a highly crystalline limestone of complex com position. T here was also present a small sill, originally dolerite, but now
GEORGE HARROW, LOWER DEE-SIDE AND HIGHLAND nORDER.
269
altered to hornblende-gneiss. The granite was present as a small but rather persistent dyke, cutting across the foliation of th e altered rocks, and from it minor intrusions were given off, though the ground was not often clear enough to allow the connection to be traced. The smaller threads cut the rocks in all directions, and it was clearly seen that the folding was completed when the granitic material consolidated. From this it follows that there can be no part of the Highland rocks in this area newer than this granite. The granite itself was seen to be pale grey, or moderatel y grey, in colour; none of it contained sufficient brown mica to give the rock a pronounced grey tint ; an invariable rule with the smaller intrusions. The party then drove a short distance to Crofthead, where similar phenomena were seen, but the amount of granite was smaller. Here a small proportion of calcareous rock was present, and the map of the district was referred to as showing the large area covered by a vast number of patches of highly altered limestone. These are all portions of the base of the bed , which is folded incessantly with th e adjace nt underlying rock so as to give the impression of a great thickness of alt ered calcareous shale. In reality, the final effect of the Highland folding is to produce a thick approximately horizontal sheet, which behaves as a new bed and maps out as such, in spite of its co mplicated internal structure. Driving on to the Mains of Tilquhilie it was intended to walk over the top of the hill, but this was rendered impossible as the ground had been recently planted. Walking along the foot of it, a great number of blocks of the granite were noted, showing how numerous the small intrusions are . Coming to more open ground, a small patch of bare rock was found in which no intrusions occurred, suppor ting the view t hat the intrusions proceed from local centres (small dyke s), and between two of these , pat ches may be found free from the granitic material. Th e little hill showed well the glacial erosion of the district, the western face being a good example of a roche moutonn ee. At this elevated point "Mr. Barrow drew attention to the form of the ground through which the Dee and the Don flow. At this distance it was not easy to distinguish the valleys of either, for the ground was comparatively low and the whole formed one area . It was explained that the form of the ground was primarily due in all probability to denudation during the epoch of the Old Red Sandstone, and the present -form was only a modification of the surfac e left when the Old Red rocks were stripped off. Indeed , it was quite possible that patches of the Old Red might still be found. The party then walked on to the Cairnshee Quarry, from which the intrusion as a whole takes its name. The opening is long and narrow and has steep sides, the intrusion being obviously
27°
GEORGE BARROW,
of a dyke-like nature. Being much larger than any of the preceding intrusions the section is deeper down below the crest of the dyke, and now for the first time we see the material of earlier consolidation from which the more acid portion has been forced out. The rock is much greyer in colour and contains far more brown mica; it is rather finer in grain because there is far more oligoclase present and this mineral occurs in smaller crystals than the bulk of the alkali-felspar, In addition, it is more markedly foliated. The walls where well exposed showed a mixture of granite and metamorphic rock, but the sides are now much more overgrown and obscured than at the time the country was surveyed. In the afternoon the party proceeded to Calladrum to examine the Newer Granite, but a halt was made on the road while Prof. Gibb drew attention to some of the glacial features that have been so well described by Mr. Bremner in his account of the history and features of the Dee Valley. (The Physical Geology of the Dee Valley, by A. Bremner, B.A., B.Sc. The University Press, Aberdeen, 1912.) From Calladrum, the north-east margin of the great mass of Newer Granite was soon reached. It is here a [me grained and obviously quickly-cooled rock, practically a quartz porphyry. Its special fine edge was explained by the fact that the edge here seen is also the original upper surface of the granite; this sloped upward rather faster than the present hill, so that further south the edge is not quite so fine in grain. Mr. Barrow stated that a similar fine edge occurred at the south-western part of the intrusion, Proceeding up the hill the Older Granite was shown in situ close to the margin of the Newer, and the same contrast in the nature of the intrusions near their margins was observed. The place was difficult to find, as the trees have gradually crept up the hill, obscuring the ground and making it almost unrecognisable. There is a better section not far off, and it is hoped someone will locate it and pile up '1 few stones to mark the site, as with a further increase in the number of trees even the section found will be untraceable. The party then descended the hill and returned to Aberdeen. SEPTE~lBER 13TH.
On the second day the party drove from Aberdeen for some miles along the south bank of the Dee and then turned southward to examine one of the larger coherent masses of the older granite. It was pointed out that there were several of these, the best known forming the Aberdeen, or Rubislaw, granite. To the south of the Dee they all form conspicuous hills, and can be identified from a great distance. The one selected for examination was that forming Kincausie Hill, and the party
LOWER DEE-SIDE AND THE HIGHLAND BORDER.
271
walked along the road that passes close to the western margin of the mass. Some exceptionally fresh sillimanite gneiss was pointed out at the commencement, close to the margin of the granite, and specimens were collected The margin was shown to be of the usual type j there is no sharp boundary to the intrusion j it consists of a mixture of granite and metamorphic rocks, the former decreasing in proportion as the main mass is left. Later a visit was made to a quarry in the main intrusion, but even here inclusions of metamorphic rock were found. The granite was seen to be moderately coarse and to contain a fair amount of brown mica but less muscovite. The party then proceeded to walk across the moor to the hill of Boswell's monument, where the ground is much more free of drift and less obscured by vegetation. The coarser pegmatite veins are much more abundant here, and, owing to the clearness of the ground, there was no difficulty in finding instances of intrusions with the finer part in the centre while the outer edge consisted of very coarse pegmatite, illustrating perfectly the extrusion of the more alkaline and slowly-cooled portion of the magma. It was pointed out that the large crystals of felspar were all alkaline j most commonly they consist of microcline j but they may also be either microperthite or orthoclase. In this area orthoclase was not often found, but in certain localities it is more abundant than microcline j no cause has been found for the change. This area is far more satisfactory for the purposes of study than that about Banchory, as the exposures are more numerous and clearer j but the Banchory area was examined to show the wide extent of the granite, the phenomena where all the intrusions are usually small, and also the margin of the newer granite by way of contrast. The party walked some distance to tea and then drove back to Aberdeen by \vay of Marywell and Craighill. SEPTE)lDER 17TH.
On this day the party travelled by train from Aberdeen to Edzell for the purpose of examining the Highland Border rocks. From Eclzell they drove up the valley of the North Esk. At Gannochy Bridge the nearly-vertical beds of the Lower Old Red Sandstone were seen in the river bed. Farther on they left the vehicles. and, with the kind permission of Colonel Mcl nroy, C. B., D. L., J. P ., followed the stream through the grounds of the Burn and examined the section which it disclosed. In deference, however, to the wishes of the proprietor no hammers were used. After traversing the Margie Series, the churned-up mass of
27 2
GEORGE BARROW,
rock above the first thrust-plane was reached. To fix the exact position of this it is necessary to find the point where small lenticles of jasper occur, and, as the rocks are all more or less red-stained, this could not easily be done without hammering. Attention was called to the resemblance of the churned-up mass of rocks to that described by Xlr. Matlev in the Lleyn peninsula. Farther on the rocks become more coherent, and large lenticular masses of infolded jasper were found associated with the greenrocks. Attention was drawn to the more massive habit of these as compared with somewhat similar rocks at Stonehaven, and Mr. Barrow explained that a series of sections had been cut from this part of the green rocks and all exhibited ophitic structure. They were in fact, intrusive sills, and the red, jasper-like aspect of the original chert was due to a slight contact alteration; in consequence of this no organisms of any kind had been detected in the North Esk jaspers. It was pointed out that the jaspers have an invariable structure when seen in microscopic sections, and are totally unlike the red infiltrated material often met with in old igneous rocks, especially if these were lavas. Later on the Margie conglomerate was reached. This is so green and often firmly cemented together that it locally looks like the green-rocks, from the detritus of which it is mostly composed. Fragments of jasper can easily be found, but are not abundant. It is thus clear that the Margie Series are newer and were originally above the Jasper and Green-rock series. The gradual and unbroken passage upward to the Margie limestone was traced in the bed of the stream. In the old quarry in which the limestone was formerly worked the small wall-like mass of dark shale above the limestone was pointed out. It is vertical, and lies in a syncline between the two outcrops of the limestones. The position of the limestone in the stream was partly visible, but the outcrop was not so clear as it sometimes is. This is due to the movements of the gravelly fragments in the river bed; a flood will sometimes almost cover the outcrop, and at others lay it almost completely bare. The actual junction of the upturned Margie shales with the Highland Rocks is not now seen; ii certainly seems advisable to have this cut open and photographed, as the work would cost only a few shillings. The party then drove on to Clattering Bridge to another quarry in the Margie limestone. The special interest of this lies in the fact that the limestone outcrop lies between the major and minor thrust-planes, which meet at the highest point or western end of the quarry. Here again the relations of the beds are rapidly becoming obscure, owing to decomposition and the pouring down of scree or detrita from the side to the bottom of the quarry. The most interesting outcrop of the limestone is now completely covered, and the bed would probably not have
LOWER D E E-S ID E A N D THE H IG H LAN D 1l0RDLR.
273
been seen at all j but, fortunatel y, Dr. Campbell , who had recently visited it, pointed out a small but clear outcrop close to the minor thrust-pl ane, or on the opposite side of the quarry to th at on which it had been sought for. A series of specimen s were collected here, as thi s will probably be also buried under scree. During the drive from the North E sk Dr. Campbell and NIr. Barrow pointed out man y interestin g points connected with the gl aciation of the rocks along the margin of the Highl an ds, including a number of dr y valleys in th e Old Red Conglomerates . A specially fine series of old mar ginal channels occurs in the H ighl and Rocks close to Cla tter ing Br idge, and they were poin ted out by Mr. Bar row, but there was not time to visit them. THE NORTH ESK. By ALFRED HARKER , M.A., F.R.S., F.G.S. SEPTEMBER
18TH.
A PARTY of five, guid ed by Mr. Barrow, went from Ed zell up the North Esk Ri ver to study th e increasing metamorphi sm in t he Highland Schists when followed away from th e Highlan d border. The section was taken up at th e p oint where th e pa rty of th e preceding day had sto pped, i.e. , at th e relatively littl ealter ed slates which ar e th rown against th e rocks of th e Mar gie Series. The a rgillaceous ba nds , which occ ur as numero us infolds in th e preval ent grits, were found to exhibit increa sing metamorphism when tr aced northward; the brown mica soon making its appearance, and forming incr easingly larger spots or pe llets, while the rocks th emselves becam e more evidently crystalline. T he eastern bank of the river was followed as fa r as the mouth of th e Burn of Mooran. The part y then crossed the river , and p roceeded up the ridge which lies N.W. of the fa rm of Co rnesc orn. The rocks fi rst encounte red wer e in the ga rnet zone, which foll ows the biot ite zone in Mr . Barrow 's scheme. The ga rnets became more conspicuous, a nd th e rocks grad ually assume d a more crystalline aspect , until the appea ra nce of staurolite marked th e coming on of th e next zone. T he staurolite crystals, including the characteristic cross-twins, are here developed in great numb er and size, and show out pr omin entl y on weathered surfaces of th e rocks. Time did not suffice for examining the cyanite zone, which should next succeed. This is th erefore the onlv one of Mr. Barrow's zones of met amorphi sm which has not' been verified and studied by the party during this excursion; th e most high ly met amorphosed rocks, characterised by sillimanite, having been already well seen ab out Banch ory and Ab erd een.
1.
LOWER DEE-SIDE AND THE HIGHLAND BORDER. By
GEOR GE B ARROW,
F.G. S.
S EPT EM IlE I{ 12T H .
THE party, which numbered 4 7 in a ll, pro ceeded by train up the Dee Valley to Ba nchory. During the jou rney, attent ion was d rawn to th e great mass es of Glaci al Gravels with which th e lower part of th e Dee Valley was filled. I n th ese, a number of terraces have been cut by streams flowing from the two edges of the local valley glacier that brought down th e gravels; as th e glacier diminished in size the terraces were gradually cut at a lower and lower level. While driving to th e first haltin g place, som e heaps of crystalline limestone by the road-side were pointed out. In many of th ese microscopic crystals of fosterite may be fou nd, perfectl y fresh, as they have been obtained from a quarr y ; in outcrop specimens the mineral is rar ely ide ntifiable. T he first halt was mad e at Beltcraig Farm , a littl e east of th e Fe uch Bridge. It was now explained th at th e da y's work would be divided into two parts; in th e morning it would be shown that th e metamorphic rocks over a large area were penetrated by a vast nu mber of small intru sions of granitic material belonging to a part of the Older Granites (the Cairnshee Granite) . Though often mere threads, they never have chilled margins, but are always granitic ; in some cases th e whole thickness of a small intrusion may be mad e of a singl e crystal of felspar. In the afternoon the margin of one of the Newer Gran ite masses wo uld be examined, and though the mass (the Kincardineshire Grani te) covers an area of over 10 0 square miles, its northeastern edge would be found to possess a fi ne grained a nd q uickly-cooled edge . T here must thu s have been a great cha nge in condition s between th e time of the two intru sion s, repr esent ing a lon g interval of tim e. The metamorphic rocks see n at Beltcraig were stated to belong to th e lowest known portion of th e H ighland series ; being below any that occur alon g the Highland border. They originally consisted of sandy shale, shale and an impure limestone (th e Dee-side limestone) ; these were here altered to gneisses, th e first con taining much felspar and often some sillimanite, th e second containing usually a great quantity of silliman ite in minute need les (fibrolite), while th e th ird was now a highly crystalline limestone of complex com position. T here was also present a small sill, originally dolerite, but now
GEORGE HARROW, LOWER DEE-SIDE AND HIGHLAND nORDER.
269
altered to hornblende-gneiss. The granite was present as a small but rather persistent dyke, cutting across the foliation of th e altered rocks, and from it minor intrusions were given off, though the ground was not often clear enough to allow the connection to be traced. The smaller threads cut the rocks in all directions, and it was clearly seen that the folding was completed when the granitic material consolidated. From this it follows that there can be no part of the Highland rocks in this area newer than this granite. The granite itself was seen to be pale grey, or moderatel y grey, in colour; none of it contained sufficient brown mica to give the rock a pronounced grey tint ; an invariable rule with the smaller intrusions. The party then drove a short distance to Crofthead, where similar phenomena were seen, but the amount of granite was smaller. Here a small proportion of calcareous rock was present, and the map of the district was referred to as showing the large area covered by a vast number of patches of highly altered limestone. These are all portions of the base of the bed , which is folded incessantly with th e adjace nt underlying rock so as to give the impression of a great thickness of alt ered calcareous shale. In reality, the final effect of the Highland folding is to produce a thick approximately horizontal sheet, which behaves as a new bed and maps out as such, in spite of its co mplicated internal structure. Driving on to the Mains of Tilquhilie it was intended to walk over the top of the hill, but this was rendered impossible as the ground had been recently planted. Walking along the foot of it, a great number of blocks of the granite were noted, showing how numerous the small intrusions are . Coming to more open ground, a small patch of bare rock was found in which no intrusions occurred, suppor ting the view t hat the intrusions proceed from local centres (small dyke s), and between two of these , pat ches may be found free from the granitic material. Th e little hill showed well the glacial erosion of the district, the western face being a good example of a roche moutonn ee. At this elevated point "Mr. Barrow drew attention to the form of the ground through which the Dee and the Don flow. At this distance it was not easy to distinguish the valleys of either, for the ground was comparatively low and the whole formed one area . It was explained that the form of the ground was primarily due in all probability to denudation during the epoch of the Old Red Sandstone, and the present -form was only a modification of the surfac e left when the Old Red rocks were stripped off. Indeed , it was quite possible that patches of the Old Red might still be found. The party then walked on to the Cairnshee Quarry, from which the intrusion as a whole takes its name. The opening is long and narrow and has steep sides, the intrusion being obviously
27°
GEORGE BARROW,
of a dyke-like nature. Being much larger than any of the preceding intrusions the section is deeper down below the crest of the dyke, and now for the first time we see the material of earlier consolidation from which the more acid portion has been forced out. The rock is much greyer in colour and contains far more brown mica; it is rather finer in grain because there is far more oligoclase present and this mineral occurs in smaller crystals than the bulk of the alkali-felspar, In addition, it is more markedly foliated. The walls where well exposed showed a mixture of granite and metamorphic rock, but the sides are now much more overgrown and obscured than at the time the country was surveyed. In the afternoon the party proceeded to Calladrum to examine the Newer Granite, but a halt was made on the road while Prof. Gibb drew attention to some of the glacial features that have been so well described by Mr. Bremner in his account of the history and features of the Dee Valley. (The Physical Geology of the Dee Valley, by A. Bremner, B.A., B.Sc. The University Press, Aberdeen, 1912.) From Calladrum, the north-east margin of the great mass of Newer Granite was soon reached. It is here a [me grained and obviously quickly-cooled rock, practically a quartz porphyry. Its special fine edge was explained by the fact that the edge here seen is also the original upper surface of the granite; this sloped upward rather faster than the present hill, so that further south the edge is not quite so fine in grain. Mr. Barrow stated that a similar fine edge occurred at the south-western part of the intrusion, Proceeding up the hill the Older Granite was shown in situ close to the margin of the Newer, and the same contrast in the nature of the intrusions near their margins was observed. The place was difficult to find, as the trees have gradually crept up the hill, obscuring the ground and making it almost unrecognisable. There is a better section not far off, and it is hoped someone will locate it and pile up '1 few stones to mark the site, as with a further increase in the number of trees even the section found will be untraceable. The party then descended the hill and returned to Aberdeen. SEPTE~lBER 13TH.
On the second day the party drove from Aberdeen for some miles along the south bank of the Dee and then turned southward to examine one of the larger coherent masses of the older granite. It was pointed out that there were several of these, the best known forming the Aberdeen, or Rubislaw, granite. To the south of the Dee they all form conspicuous hills, and can be identified from a great distance. The one selected for examination was that forming Kincausie Hill, and the party
LOWER DEE-SIDE AND THE HIGHLAND BORDER.
271
walked along the road that passes close to the western margin of the mass. Some exceptionally fresh sillimanite gneiss was pointed out at the commencement, close to the margin of the granite, and specimens were collected The margin was shown to be of the usual type j there is no sharp boundary to the intrusion j it consists of a mixture of granite and metamorphic rocks, the former decreasing in proportion as the main mass is left. Later a visit was made to a quarry in the main intrusion, but even here inclusions of metamorphic rock were found. The granite was seen to be moderately coarse and to contain a fair amount of brown mica but less muscovite. The party then proceeded to walk across the moor to the hill of Boswell's monument, where the ground is much more free of drift and less obscured by vegetation. The coarser pegmatite veins are much more abundant here, and, owing to the clearness of the ground, there was no difficulty in finding instances of intrusions with the finer part in the centre while the outer edge consisted of very coarse pegmatite, illustrating perfectly the extrusion of the more alkaline and slowly-cooled portion of the magma. It was pointed out that the large crystals of felspar were all alkaline j most commonly they consist of microcline j but they may also be either microperthite or orthoclase. In this area orthoclase was not often found, but in certain localities it is more abundant than microcline j no cause has been found for the change. This area is far more satisfactory for the purposes of study than that about Banchory, as the exposures are more numerous and clearer j but the Banchory area was examined to show the wide extent of the granite, the phenomena where all the intrusions are usually small, and also the margin of the newer granite by way of contrast. The party walked some distance to tea and then drove back to Aberdeen by \vay of Marywell and Craighill. SEPTE)lDER 17TH.
On this day the party travelled by train from Aberdeen to Edzell for the purpose of examining the Highland Border rocks. From Eclzell they drove up the valley of the North Esk. At Gannochy Bridge the nearly-vertical beds of the Lower Old Red Sandstone were seen in the river bed. Farther on they left the vehicles. and, with the kind permission of Colonel Mcl nroy, C. B., D. L., J. P ., followed the stream through the grounds of the Burn and examined the section which it disclosed. In deference, however, to the wishes of the proprietor no hammers were used. After traversing the Margie Series, the churned-up mass of
27 2
GEORGE BARROW,
rock above the first thrust-plane was reached. To fix the exact position of this it is necessary to find the point where small lenticles of jasper occur, and, as the rocks are all more or less red-stained, this could not easily be done without hammering. Attention was called to the resemblance of the churned-up mass of rocks to that described by Xlr. Matlev in the Lleyn peninsula. Farther on the rocks become more coherent, and large lenticular masses of infolded jasper were found associated with the greenrocks. Attention was drawn to the more massive habit of these as compared with somewhat similar rocks at Stonehaven, and Mr. Barrow explained that a series of sections had been cut from this part of the green rocks and all exhibited ophitic structure. They were in fact, intrusive sills, and the red, jasper-like aspect of the original chert was due to a slight contact alteration; in consequence of this no organisms of any kind had been detected in the North Esk jaspers. It was pointed out that the jaspers have an invariable structure when seen in microscopic sections, and are totally unlike the red infiltrated material often met with in old igneous rocks, especially if these were lavas. Later on the Margie conglomerate was reached. This is so green and often firmly cemented together that it locally looks like the green-rocks, from the detritus of which it is mostly composed. Fragments of jasper can easily be found, but are not abundant. It is thus clear that the Margie Series are newer and were originally above the Jasper and Green-rock series. The gradual and unbroken passage upward to the Margie limestone was traced in the bed of the stream. In the old quarry in which the limestone was formerly worked the small wall-like mass of dark shale above the limestone was pointed out. It is vertical, and lies in a syncline between the two outcrops of the limestones. The position of the limestone in the stream was partly visible, but the outcrop was not so clear as it sometimes is. This is due to the movements of the gravelly fragments in the river bed; a flood will sometimes almost cover the outcrop, and at others lay it almost completely bare. The actual junction of the upturned Margie shales with the Highland Rocks is not now seen; ii certainly seems advisable to have this cut open and photographed, as the work would cost only a few shillings. The party then drove on to Clattering Bridge to another quarry in the Margie limestone. The special interest of this lies in the fact that the limestone outcrop lies between the major and minor thrust-planes, which meet at the highest point or western end of the quarry. Here again the relations of the beds are rapidly becoming obscure, owing to decomposition and the pouring down of scree or detrita from the side to the bottom of the quarry. The most interesting outcrop of the limestone is now completely covered, and the bed would probably not have
LOWER D E E-S ID E A N D THE H IG H LAN D 1l0RDLR.
273
been seen at all j but, fortunatel y, Dr. Campbell , who had recently visited it, pointed out a small but clear outcrop close to the minor thrust-pl ane, or on the opposite side of the quarry to th at on which it had been sought for. A series of specimen s were collected here, as thi s will probably be also buried under scree. During the drive from the North E sk Dr. Campbell and NIr. Barrow pointed out man y interestin g points connected with the gl aciation of the rocks along the margin of the Highl an ds, including a number of dr y valleys in th e Old Red Conglomerates . A specially fine series of old mar ginal channels occurs in the H ighl and Rocks close to Cla tter ing Br idge, and they were poin ted out by Mr. Bar row, but there was not time to visit them. THE NORTH ESK. By ALFRED HARKER , M.A., F.R.S., F.G.S. SEPTEMBER
18TH.
A PARTY of five, guid ed by Mr. Barrow, went from Ed zell up the North Esk Ri ver to study th e increasing metamorphi sm in t he Highland Schists when followed away from th e Highlan d border. The section was taken up at th e p oint where th e pa rty of th e preceding day had sto pped, i.e. , at th e relatively littl ealter ed slates which ar e th rown against th e rocks of th e Mar gie Series. The a rgillaceous ba nds , which occ ur as numero us infolds in th e preval ent grits, were found to exhibit increa sing metamorphism when tr aced northward; the brown mica soon making its appearance, and forming incr easingly larger spots or pe llets, while the rocks th emselves becam e more evidently crystalline. T he eastern bank of the river was followed as fa r as the mouth of th e Burn of Mooran. The part y then crossed the river , and p roceeded up the ridge which lies N.W. of the fa rm of Co rnesc orn. The rocks fi rst encounte red wer e in the ga rnet zone, which foll ows the biot ite zone in Mr . Barrow 's scheme. The ga rnets became more conspicuous, a nd th e rocks grad ually assume d a more crystalline aspect , until the appea ra nce of staurolite marked th e coming on of th e next zone. T he staurolite crystals, including the characteristic cross-twins, are here developed in great numb er and size, and show out pr omin entl y on weathered surfaces of th e rocks. Time did not suffice for examining the cyanite zone, which should next succeed. This is th erefore the onlv one of Mr. Barrow's zones of met amorphi sm which has not' been verified and studied by the party during this excursion; th e most high ly met amorphosed rocks, characterised by sillimanite, having been already well seen ab out Banch ory and Ab erd een.