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Field meeting at Weymouth, Dorset
141
FIELD MEETING AT WEYMOUTH, DORSET Saturday, 13th September, to Friday, 19th September, 1947 Report by the Director: P. C. Sylvester-Bradley. [Received 28th January. 1948]
THE object of the meeting, whose headquarters were at the Riviera Hotel, Bowleaze Cove, was to study the Jurassic stratigraphy and the tectonics of the Weymouth and Bridport district. Thirtyfive members and friends attended on one or more days, the average being 22. Saturday, 13th September REDCLIFF AND JORDAN CLIFF, BOWLEAZE COVE In the afternoon a party walked along the foreshore from Bowleaze Cove to Redcliff Point. The shore is strewn with large blocks of Preston Grit, and with doggers from the Bencliff Grit above. Many fossils, including several ammonites, were chiselled out of the former, and the striking U-shaped worm tubes displayed in the latter excited comment. The party returned by way of the clifftop. After tea, the Oxford Clay of Jordan Cliff was searched for fossils and yielded numerous large Gryphaea di/atata, many crushed ammonites and a variety of lamellibranchs, including Cercomya. The Serpula Bed noted by Damon (1884, p. 29*) made a conspicuous band at the foot of the cliff. Sunday, 14th September] INFERIOR OOLITE OF BURTON BRADSTOCKBEAMINSTER DISTRICT The party travelled by coach to Bothenhampton, near Bridport, where Brigadier G. Bomford exhibited fossils he had collected from localities to be visited later in the day. His remarkable collection was greatly admired. From Bothenhampton the coach conveyed the party to Burton Bradstock, where the lane-side section of Cliff Hill was explained by the Director, and many ammonites and other fossils were collected. Owing to an unfortunately late start there was insufficient time to collect from the fallen blocks on the shore, as had been intended. After lunch the coach moved on via Shipton Gorge to Stoney Head quarry. Here some piles of ammonites had been made by the quarrymen, mostly Parkinsonia spp. from the Top Beds, but * For list of References, see p, 147. t It had originally been planned to visit Worbarrow and Kimeridge on this day, but as minefields still remained uncleared at both these places, the following programme was substituted.
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P. C. SYLVESTER-BRADLEY
also some leioceratids from the base of the Red Bed. The party then proceeded to the quarries at Loder's Cross, where the zigzag bed, the obliqua bed and the base of the Red Bed were all found to be gratifyingly fossiliferous. The coach continued northwards by bye-roads to Coombe Quarry, Mapperton, where interest centred on the discites bed. The final quarry of the day was the famous Horn Park Quarry, between Beaminster and Broadwindsor, where abundant ammonites were obtained from the so-called Building Stones of the murchisonae zone. A vote of thanks was returned to Brigadier Bomford for his helpful demonstrations both at his home and in the quarries. Monday, 15th September HOLWORTH, RINGSTEAD AND OSMINGTON MILLS
The coach dropped the party at the top of Spring Bottom Hill, where the Director explained the structural features of the view. The hill is capped by a narrow spur of chalk, which follows the axis of the Spring Bottom syncline. This syncline does not conform to the folding of the Jurassic rocks beneath. To the north the chalk has been denuded from a broad anticline which covered unconformably the more tightly packed Upton syncline and Poxwell pericline. To the south the Kimeridge Clay and Corallian Beds are involved in the easternmost extension of the Weymouth anticline, whose gently dipping southern limb can be seen on the skyline in the strike section of Portland. The party walked along the turf of the down to Holworth, where sections of Lower Purbeck, Portland Stone and Portland Sand were examined. A good section of Kimeridge Clay exposed below the quarry was too dry to yield many of its fossils. A scramble through the brambles of the land-slipped undercliff led back to the path, whence an excellent view of the White Nothe unconformity was seen. The party then descended to the beach and walked along the shingle to Ringstead, where the ebbing tide exposed the rocks of Ringstead Ledges. The low cliffs of Ringstead yielded abundant fossils from the Coral Bed and the clays above. Proceeding along the shore to Bran Point, the reefs in the Trigonia clavellata beds were examined, and the detailed section of the Osmington Oolite worked out. The Bran Point fault could be followed clearly with the aid of Arkell's 25in. map, copies of which had been distributed (Arkell, 1936, Fig. 1). The succeeding beds of the Corallian sequence were passed over on the way along the rock-strewn shore to Osmington Mills, where some members continued a little to the westwards to examine the well-known structures displayed on the foreshore at low tide. The party re-assembled at the Picnic Inn. Some then returned to Bowleaze Cove by bus ; the rest walked back along the cliff path.
FIELD MEETING AT WEYMOUTH, DORSET
143
Tuesday, 16th September ISLE OF PORTLAND By the courtesy of Mr. W. J. Sansom, of the Bath and Portland Stone Firms Ltd., the party was shown first round the Masons' Yard-the largest of its kind in the world-and then around the " Fossil Garden," decorated with petrified trees from the Purbeck Beds, fossil "birds' nests" (Cycadeoidea), Portland roach, and, on every side, huge ammonites (Titanites) known to the quarrymen as fossil eels. From here the guide conducted the party round two of the quarries, demonstrating both the succession and the methods of working. After lunch at Portland Bill, the Raised Beach and its associated deposits were examined. In the neighbourhood of the Bill the methods of strip-cultivation were pointed out by the Director. An interesting point about this system as developed in Portland, recently demonstrated by Lt.-Col. C. D. Drew, is the presence of turf balks between the "lands" of the field. Orwin (1938) has denied the existence of such balks in typical "open fields." Strip-cultivation was probably not typical in Portland, on account of the custom of " Gavelkind" (equal inheritance) which for a long time prevailed on the Island, and which suggests points of comparison with the strip fields of France. In Portland, the" lands" (strips) are termed" lawns" and the turf" balks" are" lawn-sheds." This survival of feudal England is typical of the conservative habits of the Portlanders, who still refer to the rest of the world as "Kimberlins," in the same way that the Jews talk of Gentiles, or the Romans referred to barbarians. On the way back from the Bill, the coach stopped above Fortuneswell, and the party dismounted to see the magnificent view of the Chesil Beach and the Weymouth peninsula. The coach stopped again at Chesilton, and some of the party scrambled up Chesil Beach to examine its character at this, its most southerly point.
CmCKERELL The coach then took the party to Messrs. Webb, Major and Co.'s brickpits at Crook Hill, Chickerell. Many crushed Kosmoceras spp, and Meleagrinella were obtained, and a few mudstone casts of the body chambers of Peltoceras and other ammonites. "Turtle Stones" (septarian concretions) and selenite crystals littered the floor of the pit. LANGTON HERRING The party left the coach at Langton Herring and walked to Herbury, where countless shells of Goniorhynchia boueti and its associates washed out of the Boueti Bed lie on the shores of the Fleet. Ostrea hebridica and its variety elongata were collected from the lumachelle on the way to the coastguard station, where the party rejoined the coach for the return journey to Bowleaze.
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P. C. SYLVESTER-BRADLEY
Wednesday, 17th September LULWORTH DISTRICT The party journeyed by coach to Weymouth pier and embarked in a boat, the cliff sections being admirably visible (see Fig. 15). The party landed by dinghy in Mupe Bay, where the gradual transition between Purbeck and Wealden was pointed out. After lunch, eaten on the ledges of Purbeck Marble and Unio Beds that form the inner part of Mupe Reefs, the Purbeck Beds of Bacon Hole were explored. Special attention was paid to the fine section of Broken Beds, and Forbes' " Pecten Seam" was quickly located some nine feet above the Cinder Bed. The uppermost Purbeck, with thin limestones crowded with Cypridea adjuncta, was examined on the walk round to the Fossil Forest. The sections of Broken Beds shown at the Fossil Forest and Lulworth Cove were compared with those seen at Bacon Hole. ,, ,
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The peculiar fault in the chalk of Lulworth Cove gave rise to some speculation. After tea Stair Hole was visited, and the party then re-embarked and sailed past Dungy Head and Durdle Door to Durdle Cove, where most members disembarked to visit the fine sections of Upper Greensand and Lower to Middle Chalk there exposed. The journey back to Weymouth harbour was accomplished without event. Thus ended a day spent along a coast-line combining unsurpassed scenic beauty with the almost startling clarity of serial sections cut by the sea through the Purbeck Fold. Thursday, 18th September WATTON CLIFF, EYPE AND SEATOWN The coach proceeded by the coastal road via Abbotsbury and Burton Bradstock to Eype Mouth. After spending some time at Watton Cliff collecting from the Wattonensis Beds of the Fuller's Earth, from the Forest Marble, and from an Ostrea lumachelle, there caught up in the fault, the party walked along the shore beneath Thorncombe Beacon, Doghouse Hill and Down Cliff, collecting
FIELD MEETING AT WEYMOUTH, DORSET
from the many fallen blocks interest was aroused by the of its famous brittle-stars. ammonites. Blocks of the easily identified.
145
of Middle and Upper Lias. Greatest Starfish Bed, which displayed many The Junction Bed was full of worn Margaritatus Bed were not always
ST. GABRIEL'S TO CHARMOUTH Lunch was eaten in the little inn at Seatown . The coach then took the party through Chideock to the cross-lanes near St. Gabriel's Farm, on the west side of Golden Cap . Dr. W. D. Lang met the party at St. Gabriel's Mouth and conducted them over the sections of Lower Lias to Charmouth. Ammonites and belemnites indicative of the several zones displayed by the Green Ammonite Beds, the Belemnite Marls and the Black Marls were collected en route, and the remarkably fine exposure at present displayed by the cliffs of the Ridge Faults was pointed out. At Charmouth the contorted shales in the valley were compared to those seen earlier in the day at Eype Mouth and Seatown. These contortions at Charmouth and Seatown have been attributed to "valley bulge" (Hollingworth, Taylor and Kellaway, 1944, pp. 30, 42, and Lang, in discussion of the same, pp. 38-40). Their occurrence at Eype Mouth gives additional evidence for regarding their origin as superficial. Friday, 19th September ABBOTSBURY The coach took the party via Langton Herring and Rodden to the hill above New Barn, and some members walked in torrential rain to Shipmoor Point and collected typical brachiopods of the Upper and Lower Cornbrash, together with Pholadomya and Meleagrinella echinata. Proceeding by coach to Abbotsbury, members visited the sections of Kimeridgian Iron Ore at Red Lane and collected fossils. The bus then went up Wears Hill on the Swyre road to the turning to Bexington Farm, where a very fossiliferous brachiopod bed in the Forest Marble yielded as yet undescribed species. The effects of the Abbotsbury fault were demonstrated, the Abbotsbury Iron Ore being brought into juxtaposition with Forest Marble. UPWEY AND BINCOMBE From Abbotsbury the coach travelled through Portesham and Friar Waddon to Upwey Wishing Well. The tectonics displayed in quarries in Purbeck Beds and Chalk on each side of the Ridgeway Fault were examined, and then the coach moved to Bincombe Railway Cutting between the two tunnels, where the famous Oxford Clay hoc. GBOL. Assoc., VOL. 59, PART 3, 1948.
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FIELD MEETING AT WEYMOUTH, DORSET
147
•• dyke" was visited, and fragments of Gryphaea dilatata collected. The adjacent Purbeck Beds were noted, the Cinder Bed being quickly recognised.
CHALBURY TO SUTTON POYNTZ The party left the coach at Chalbury Quarries to examine the Purbeck and Portland Beds ; giant ammonites were seen in situ in the Cherty Series of the Portlandian. Walking towards Greenhill Barton, members then saw that the tufas near the base of the Purbeckian form a scar, below which the scar of the Exogyra Bed in the Portland Sands was picked up. This bed proved useful in working out the tectonics of the highly complicated zone bordering the fault line at Greenhill Barton. Towards Sutton Poyntz more placid geology was revealed by the copious spring which feeds the Weymouth Waterworks. The waterbearing stratum was first mapped as Greensand over Kimeridge. The Director pointed out the stream section discovered by officers of the D'Arcy Exploration Co., which showed, by the presence of Cornbrash and Forest Marble in situ, that the clay beneath the greensand was Oxford Clay.
POXWELL From Sutton Poyntz the coach took the party to the road cutting at Poxwell, where Middle Purbeck is still well displayed, and the freshwater gastropods below the Cinder Bed excited much interest. The quarry showing the junction of Portland and Purbeck near Poxwell Lodge was visited, and also a quarry in the Cypris Freestones on the other side of the road. Poxwell is perhaps the finest small scale example of a dissected pericline in the country. (See Plate 13 and Fig. 16.) In the evening votes of thanks were accorded to the Director, Mr. R. V. Melville, Mr. E. C. Martin, Brigadier G. Bomford and Dr. W. D. Lang for their services to the meeting on Sunday and Thursday respectively, and to Miss P. S. Walder,who, although unfortunately unable to get to the meeting, had acted as secretary at great inconvenience to herself.
REFERENCES ARKELL, W. J. 1936. The Corallian Beds of Dorset. Proc. Dorset Nat. Hist, and Arch. Soc., vol. lvii, DAMON, R. 1884. Geology of Weymouth and Portland. Second edition. HOLLINGWORTH, S. E., TAYLOR, J. H., and KELLAWAY, G. A. 1944. Largescale Superficial Structures in the Northampton Ironstone Field. Quart. Journ. Geol. Soc., vol, c. ORWIN, C. S. 1938. The Open Fields.
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G. BOMFORD
APPENDIX
NEW SECTIONS IN THE INFERIOR OOLITE By G. BOMFORD SMALL PIT N.E. OF LODER'S CROSS (30/505929) P. parkinsoni zone S. truellei subzone (7) 6. Flaggy limestone, passing up into subsoil. Procerites 7 sp. O' Terebratula " sphaeroidalis Seen to about G. garantiana subzone
ft. ins. 2
0
0
5
0
4
0
6
0
8
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8 0
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OBLIQUA BED Sb. Oolitic limestone. Parkinsonia sp., Prorsisphinctes miseres (large and common), Leptosphinctes subdivisus, Garantiana garantiana, Oppelia subradiata, O. pleurifera, Lissoceras sp., Sphaeroceras sp., belemnites, Amphitrochilia duplicata, Pictavia bajocensis, Pleurotomaria palaemon, P. bessina, Astarte obliqua, Trigonia costata, T. sp., Goniothyrls phillipsi, O' Terebratula" decipiens 7, .. Rhynchonella " sp,
Sa. Shell conglomerate. Prorsisphinctes miseres, Garantiana garantiana (common), G. aff. althoffi 7, Oppelia pulchra Stephanoceras sp., Poecilimorphus sp., Spiroceras toxoconicum, S. wattoni, Pictavia bajocensis, Pleurotomaria palaemon, Ataphrus sp., Cerithium" sp., Pseudomelania sp., Astarte obliqua, A. sp., Cucullaea cf. oblonga, Nucula sp., Entolium sp., O'
Goniomya literata, Coelopis lunulata, O' Terebratula " decipiens, Ptychothyris stephani, Pygorhytis ringens.i,
Planed surface S. humphriesianum zone 4. Teloceras found in a soft matrix in a hollow in the top of Bed 3b S. sowerbyi (and O. sauzei 7) zone RED BED 3b. Limestone with small red ooliths. Few fossils 3a. Limestone with large red ooliths and numerous snuffboxes," passing down into conglomerate. Hyperlioceras sp., Graphoceras 7 sp., Emarginula 7 sp, attached to bed below, Rhynchonella " sp, Planed surface L. opalinum zone 2. BLUE BED. Blue grey limestone. Bredya crassornata, B 7 sp., Anco/ioceras sp., Lima hersilia, Ceratomya bajociana 1. Sandy grey limestone. Leioceras sp, (7 Cypholioceras) seen to O'
O'
COOMBE QUARRY, NEAR MAPPERTON
(30/496996)
P. parkinsoni zone 6. Oolitic limestone, weathering flaggy, seen to about S. Crinoidal limestone 4. Whitish limestone, much veined with calcite Parkinsonia schloenbachi, P. parkinsoni, Stephanoceras sp., Pictavia bajocensis, Lima sp., Trigonia costata, Pinna sp., Terebratula " sphaeroidalis Planed surface O'
8
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FIELD MEETING AT WEYMOUTH, DORSET
S. sowerbyi zone 3. Red Bed. Limestone full of large red ooliths. Deltotoceras,
ft. ins.
Hyperlioceras sp., Sonninia sp., .. Cerithium " abbas?, Coelastarte excavata, Gresslya sp, lin. to Planed surface L. murchisonae zone 2. Shell conglomerate. Red ooliths. Ancolioceras sp., ? Brasilia sp., Pseudomelania bicarinata, Pleurotomaria actinomphala, Po elongata*, Gresslya sp., Pleuromya uniformis, Pholadomya jidicula*, .. Terebratula " perovalis, .. Rhynchonella " subangulata, .. Rhynchonella " sp., Montlivaltia 0 to delabechei ... L. opalinum zone l. Grey limestone with scattered yellow ooliths. Leioceras spp., Lytoceras sp., Tmetoceras scissum, Lima hersilia seen to
0
2
0
• Possibly from Bed 30 QUARRY NEAR HORN PARK (31/456020) P. parkinsoni zone 70 Top Beds. Flaggy and rubbly limestone passing up into subsoil. Lissoceras sp., Stephanoceras spp., Parkinsonia aff. schloenbachi sp., P. parkinsonis, Ataphrus laevigatus, Amphitrochilia duplicata, Cucullaea sp., Modiolus sp., Ctenostreon pectiniformis, Coelopis lunulatat; Aulacothyris carinata, .. Terebratula " sphaeroidalis, .. T." eudesi, Ptychothyris stephani, Sphenorhynchia cf. aviformis, Acanthorhynchia panacanthina, Acanthothyris spinosa, Pentacrinus, Cidaris bouchardii, Pygorhytis ringens, Holectypus hemisphericust, Seen Trochocyathus magnevillianus 'l., ° '1 S. sowerbyi or O. sauzei zone 60 Red Bed. Unfossiliferous limestone in two beds. Belemnapsis sp., Lamelliphorus ornatissimus, .. Rhynchonella " sp., Cronoid ossicles ... 5. Clay parting L. murchisonae zone G. concava and B, bradfordensis subzones 4. Limestone with numerous brown ooliths. Graphoceras spp. abundant in the upper part, Brasilia spp. in the lower Lytoceras sp., Tmetoceras sp, juv. aff, scissum S., Brasilia sublineata So, B. ambigua So, B. cf. baylei, B. simi/is So, B. giganteat So, Graphoceras aff, cavatum So, G. aff. pulchra So, G. stigmosum So, G. v-scriptum S., G. aff. concavum* S., G. rudis So, Go (Platygraphoceras) sp. juv., So, Erycites abbas S., Sonninia (Parammatoceras) sp. [uv., S., So (Fissi/obiceras) sp. juv. S., Sonninia spp., Belemnopsis blainvilleit; Amberleya ornata, Procerithium undulatum, Pseudomelania bicarinata, Littorina dorsetensiss, Discohelix altust; Ataphrus laevigatus, Pleurotomaria actinamphala, P. baugieri, P. elongata, P. yeovi/ensis, Amphitrochilia winwoodit, Grammatodon sp., Cucullaea sp.*, Myoconcha crassa, Trigonia bella?, T. costatat, T. striata", Entolium sp., Ctenostreon pectiniformis*, Ostrea sp., Astarte sp.*, Coelastarte excavatat, Trigonastarte trigonalisi, Cardium sp., Nucula? sp., Gresslya peregrina*, Pleuromya uniformls", Pseudoglossothyris ampla, .. Terebratula " eudesi, .. Rhynchonella " subangulata, Cymatorhynchia sp. nov. t Common. • Abundant.
2
8 2
7 1
6
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FIELD MEETING AT WEYMOUTH, DORSET
B. bradfordensis and L. murchisonae s.s. subzones 3. Grey limestone; ammonites with their chambers generally infilled with crystalline calcite. Tmetoceras sp. juv. aft". scissum S. Ludwigia obtusa" S., L. aft". brasili S., L. obtusiformis S., L. (Welschia) sp., Brasilia bradfordensis S., B. bayleit S., Planammatoceras planiforme S., Pseudomelania bicarinata, Trochus sp., Craterospongia concentrica. * L. murchisonae s.s, and Ancolioceras spp. subzones 2. Yellowish limestone with irregular ochreous patches. Ammonites usually preserved as casts with rotted centres '" Lytoceras (Pachylytoceras) aaleniayum" S., L. (P.) torulosumt S., Ancolioceras substriatum" S., A. costatum" S., Ludwigia obtusa S., L. aft". brasili" S., Ludwigia sp. nov. S., Brasilia sp. S., B. (" Manselia ") cf. subacuta S., " Hammatoceras" sp, S., Nautilust sp., Megateuthis giganteus, Pseudomelania sp., Natica sp. 1, Cucul/aea sp., Modiolus plicatus, Myoconcha crassa", Trigonia striata, Entolium cf. demissum", Chlamys sp, 1, Velata tuberculosa, Lima bradfordensis, L. aft". placida, L. hersilia*, Ctenostreon pectiniformis, Ostrea sp., Lopha sp., Pteroperna sp., Pinna sp., Astarte sp., Trigonastarte trigonalirt; Pseudisocardia cordata, Ceratomya bajocianat, Gresslya peregrina *, Pleuromya uniformis", Pholadomya fidicula"; " Terebratula " perovalist ; Lophrothyris etheridgii, Cincta anglica, Acanthorhynchia panacanthina, "Rhynchonel/a" spp., Discina sp., Palaeopagurus, Apiocrinus, Galeropygus agariciformis, Montlivaltia delabecheit, ? L. opalinum zone 1. Hard crystalline limestone. Many lamellibranchs and some ammonites (Leioceras), but this bed has not long been in Seen to work, and has not yet been collected
ft. ins. 2
0
2
0
0
* Abundant. t Common. Identifications by Dr. L. F. Spath are marked" S." Mr. R. V. Melville has helped with the identification of others.
FIELD MEETING AT WEYMOUTH, DORSET Saturday, 13th September, to Friday, 19th September, 1947 Report by the Director: P. C. Sylvester-Bradley. [Received 28th January. 1948]
THE object of the meeting, whose headquarters were at the Riviera Hotel, Bowleaze Cove, was to study the Jurassic stratigraphy and the tectonics of the Weymouth and Bridport district. Thirtyfive members and friends attended on one or more days, the average being 22. Saturday, 13th September REDCLIFF AND JORDAN CLIFF, BOWLEAZE COVE In the afternoon a party walked along the foreshore from Bowleaze Cove to Redcliff Point. The shore is strewn with large blocks of Preston Grit, and with doggers from the Bencliff Grit above. Many fossils, including several ammonites, were chiselled out of the former, and the striking U-shaped worm tubes displayed in the latter excited comment. The party returned by way of the clifftop. After tea, the Oxford Clay of Jordan Cliff was searched for fossils and yielded numerous large Gryphaea di/atata, many crushed ammonites and a variety of lamellibranchs, including Cercomya. The Serpula Bed noted by Damon (1884, p. 29*) made a conspicuous band at the foot of the cliff. Sunday, 14th September] INFERIOR OOLITE OF BURTON BRADSTOCKBEAMINSTER DISTRICT The party travelled by coach to Bothenhampton, near Bridport, where Brigadier G. Bomford exhibited fossils he had collected from localities to be visited later in the day. His remarkable collection was greatly admired. From Bothenhampton the coach conveyed the party to Burton Bradstock, where the lane-side section of Cliff Hill was explained by the Director, and many ammonites and other fossils were collected. Owing to an unfortunately late start there was insufficient time to collect from the fallen blocks on the shore, as had been intended. After lunch the coach moved on via Shipton Gorge to Stoney Head quarry. Here some piles of ammonites had been made by the quarrymen, mostly Parkinsonia spp. from the Top Beds, but * For list of References, see p, 147. t It had originally been planned to visit Worbarrow and Kimeridge on this day, but as minefields still remained uncleared at both these places, the following programme was substituted.
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P. C. SYLVESTER-BRADLEY
also some leioceratids from the base of the Red Bed. The party then proceeded to the quarries at Loder's Cross, where the zigzag bed, the obliqua bed and the base of the Red Bed were all found to be gratifyingly fossiliferous. The coach continued northwards by bye-roads to Coombe Quarry, Mapperton, where interest centred on the discites bed. The final quarry of the day was the famous Horn Park Quarry, between Beaminster and Broadwindsor, where abundant ammonites were obtained from the so-called Building Stones of the murchisonae zone. A vote of thanks was returned to Brigadier Bomford for his helpful demonstrations both at his home and in the quarries. Monday, 15th September HOLWORTH, RINGSTEAD AND OSMINGTON MILLS
The coach dropped the party at the top of Spring Bottom Hill, where the Director explained the structural features of the view. The hill is capped by a narrow spur of chalk, which follows the axis of the Spring Bottom syncline. This syncline does not conform to the folding of the Jurassic rocks beneath. To the north the chalk has been denuded from a broad anticline which covered unconformably the more tightly packed Upton syncline and Poxwell pericline. To the south the Kimeridge Clay and Corallian Beds are involved in the easternmost extension of the Weymouth anticline, whose gently dipping southern limb can be seen on the skyline in the strike section of Portland. The party walked along the turf of the down to Holworth, where sections of Lower Purbeck, Portland Stone and Portland Sand were examined. A good section of Kimeridge Clay exposed below the quarry was too dry to yield many of its fossils. A scramble through the brambles of the land-slipped undercliff led back to the path, whence an excellent view of the White Nothe unconformity was seen. The party then descended to the beach and walked along the shingle to Ringstead, where the ebbing tide exposed the rocks of Ringstead Ledges. The low cliffs of Ringstead yielded abundant fossils from the Coral Bed and the clays above. Proceeding along the shore to Bran Point, the reefs in the Trigonia clavellata beds were examined, and the detailed section of the Osmington Oolite worked out. The Bran Point fault could be followed clearly with the aid of Arkell's 25in. map, copies of which had been distributed (Arkell, 1936, Fig. 1). The succeeding beds of the Corallian sequence were passed over on the way along the rock-strewn shore to Osmington Mills, where some members continued a little to the westwards to examine the well-known structures displayed on the foreshore at low tide. The party re-assembled at the Picnic Inn. Some then returned to Bowleaze Cove by bus ; the rest walked back along the cliff path.
FIELD MEETING AT WEYMOUTH, DORSET
143
Tuesday, 16th September ISLE OF PORTLAND By the courtesy of Mr. W. J. Sansom, of the Bath and Portland Stone Firms Ltd., the party was shown first round the Masons' Yard-the largest of its kind in the world-and then around the " Fossil Garden," decorated with petrified trees from the Purbeck Beds, fossil "birds' nests" (Cycadeoidea), Portland roach, and, on every side, huge ammonites (Titanites) known to the quarrymen as fossil eels. From here the guide conducted the party round two of the quarries, demonstrating both the succession and the methods of working. After lunch at Portland Bill, the Raised Beach and its associated deposits were examined. In the neighbourhood of the Bill the methods of strip-cultivation were pointed out by the Director. An interesting point about this system as developed in Portland, recently demonstrated by Lt.-Col. C. D. Drew, is the presence of turf balks between the "lands" of the field. Orwin (1938) has denied the existence of such balks in typical "open fields." Strip-cultivation was probably not typical in Portland, on account of the custom of " Gavelkind" (equal inheritance) which for a long time prevailed on the Island, and which suggests points of comparison with the strip fields of France. In Portland, the" lands" (strips) are termed" lawns" and the turf" balks" are" lawn-sheds." This survival of feudal England is typical of the conservative habits of the Portlanders, who still refer to the rest of the world as "Kimberlins," in the same way that the Jews talk of Gentiles, or the Romans referred to barbarians. On the way back from the Bill, the coach stopped above Fortuneswell, and the party dismounted to see the magnificent view of the Chesil Beach and the Weymouth peninsula. The coach stopped again at Chesilton, and some of the party scrambled up Chesil Beach to examine its character at this, its most southerly point.
CmCKERELL The coach then took the party to Messrs. Webb, Major and Co.'s brickpits at Crook Hill, Chickerell. Many crushed Kosmoceras spp, and Meleagrinella were obtained, and a few mudstone casts of the body chambers of Peltoceras and other ammonites. "Turtle Stones" (septarian concretions) and selenite crystals littered the floor of the pit. LANGTON HERRING The party left the coach at Langton Herring and walked to Herbury, where countless shells of Goniorhynchia boueti and its associates washed out of the Boueti Bed lie on the shores of the Fleet. Ostrea hebridica and its variety elongata were collected from the lumachelle on the way to the coastguard station, where the party rejoined the coach for the return journey to Bowleaze.
144
P. C. SYLVESTER-BRADLEY
Wednesday, 17th September LULWORTH DISTRICT The party journeyed by coach to Weymouth pier and embarked in a boat, the cliff sections being admirably visible (see Fig. 15). The party landed by dinghy in Mupe Bay, where the gradual transition between Purbeck and Wealden was pointed out. After lunch, eaten on the ledges of Purbeck Marble and Unio Beds that form the inner part of Mupe Reefs, the Purbeck Beds of Bacon Hole were explored. Special attention was paid to the fine section of Broken Beds, and Forbes' " Pecten Seam" was quickly located some nine feet above the Cinder Bed. The uppermost Purbeck, with thin limestones crowded with Cypridea adjuncta, was examined on the walk round to the Fossil Forest. The sections of Broken Beds shown at the Fossil Forest and Lulworth Cove were compared with those seen at Bacon Hole. ,, ,
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FIG, 15.-euFF SECl10N BETWEEN HOLWORTH AND BAT'S HEAD, showing the intra-Cretaceous unconformity and the fore syncline of the Purbeck Fold. Vertical scale exaggerated. After Strahan and Arkell, with modifications.
The peculiar fault in the chalk of Lulworth Cove gave rise to some speculation. After tea Stair Hole was visited, and the party then re-embarked and sailed past Dungy Head and Durdle Door to Durdle Cove, where most members disembarked to visit the fine sections of Upper Greensand and Lower to Middle Chalk there exposed. The journey back to Weymouth harbour was accomplished without event. Thus ended a day spent along a coast-line combining unsurpassed scenic beauty with the almost startling clarity of serial sections cut by the sea through the Purbeck Fold. Thursday, 18th September WATTON CLIFF, EYPE AND SEATOWN The coach proceeded by the coastal road via Abbotsbury and Burton Bradstock to Eype Mouth. After spending some time at Watton Cliff collecting from the Wattonensis Beds of the Fuller's Earth, from the Forest Marble, and from an Ostrea lumachelle, there caught up in the fault, the party walked along the shore beneath Thorncombe Beacon, Doghouse Hill and Down Cliff, collecting
FIELD MEETING AT WEYMOUTH, DORSET
from the many fallen blocks interest was aroused by the of its famous brittle-stars. ammonites. Blocks of the easily identified.
145
of Middle and Upper Lias. Greatest Starfish Bed, which displayed many The Junction Bed was full of worn Margaritatus Bed were not always
ST. GABRIEL'S TO CHARMOUTH Lunch was eaten in the little inn at Seatown . The coach then took the party through Chideock to the cross-lanes near St. Gabriel's Farm, on the west side of Golden Cap . Dr. W. D. Lang met the party at St. Gabriel's Mouth and conducted them over the sections of Lower Lias to Charmouth. Ammonites and belemnites indicative of the several zones displayed by the Green Ammonite Beds, the Belemnite Marls and the Black Marls were collected en route, and the remarkably fine exposure at present displayed by the cliffs of the Ridge Faults was pointed out. At Charmouth the contorted shales in the valley were compared to those seen earlier in the day at Eype Mouth and Seatown. These contortions at Charmouth and Seatown have been attributed to "valley bulge" (Hollingworth, Taylor and Kellaway, 1944, pp. 30, 42, and Lang, in discussion of the same, pp. 38-40). Their occurrence at Eype Mouth gives additional evidence for regarding their origin as superficial. Friday, 19th September ABBOTSBURY The coach took the party via Langton Herring and Rodden to the hill above New Barn, and some members walked in torrential rain to Shipmoor Point and collected typical brachiopods of the Upper and Lower Cornbrash, together with Pholadomya and Meleagrinella echinata. Proceeding by coach to Abbotsbury, members visited the sections of Kimeridgian Iron Ore at Red Lane and collected fossils. The bus then went up Wears Hill on the Swyre road to the turning to Bexington Farm, where a very fossiliferous brachiopod bed in the Forest Marble yielded as yet undescribed species. The effects of the Abbotsbury fault were demonstrated, the Abbotsbury Iron Ore being brought into juxtaposition with Forest Marble. UPWEY AND BINCOMBE From Abbotsbury the coach travelled through Portesham and Friar Waddon to Upwey Wishing Well. The tectonics displayed in quarries in Purbeck Beds and Chalk on each side of the Ridgeway Fault were examined, and then the coach moved to Bincombe Railway Cutting between the two tunnels, where the famous Oxford Clay hoc. GBOL. Assoc., VOL. 59, PART 3, 1948.
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FIG. 16 (in explanation of PI. 13).-TIIE POXWELL PERICLINE Geological lines after W. J. Arkell ; g 12 Kimeridge Clay; g 13' Portland Sand; g 13 Portland Stone; g 14' Lower Purbeck Beds; g 14"_'" Middle and Upper Purbeck Beds ; h I Wealden; h 3-4 Gault and Upper Greensand i h 5 Chalk. Scale: the map measures 1 x 1.6 miles. K
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FIELD MEETING AT WEYMOUTH, DORSET
147
•• dyke" was visited, and fragments of Gryphaea dilatata collected. The adjacent Purbeck Beds were noted, the Cinder Bed being quickly recognised.
CHALBURY TO SUTTON POYNTZ The party left the coach at Chalbury Quarries to examine the Purbeck and Portland Beds ; giant ammonites were seen in situ in the Cherty Series of the Portlandian. Walking towards Greenhill Barton, members then saw that the tufas near the base of the Purbeckian form a scar, below which the scar of the Exogyra Bed in the Portland Sands was picked up. This bed proved useful in working out the tectonics of the highly complicated zone bordering the fault line at Greenhill Barton. Towards Sutton Poyntz more placid geology was revealed by the copious spring which feeds the Weymouth Waterworks. The waterbearing stratum was first mapped as Greensand over Kimeridge. The Director pointed out the stream section discovered by officers of the D'Arcy Exploration Co., which showed, by the presence of Cornbrash and Forest Marble in situ, that the clay beneath the greensand was Oxford Clay.
POXWELL From Sutton Poyntz the coach took the party to the road cutting at Poxwell, where Middle Purbeck is still well displayed, and the freshwater gastropods below the Cinder Bed excited much interest. The quarry showing the junction of Portland and Purbeck near Poxwell Lodge was visited, and also a quarry in the Cypris Freestones on the other side of the road. Poxwell is perhaps the finest small scale example of a dissected pericline in the country. (See Plate 13 and Fig. 16.) In the evening votes of thanks were accorded to the Director, Mr. R. V. Melville, Mr. E. C. Martin, Brigadier G. Bomford and Dr. W. D. Lang for their services to the meeting on Sunday and Thursday respectively, and to Miss P. S. Walder,who, although unfortunately unable to get to the meeting, had acted as secretary at great inconvenience to herself.
REFERENCES ARKELL, W. J. 1936. The Corallian Beds of Dorset. Proc. Dorset Nat. Hist, and Arch. Soc., vol. lvii, DAMON, R. 1884. Geology of Weymouth and Portland. Second edition. HOLLINGWORTH, S. E., TAYLOR, J. H., and KELLAWAY, G. A. 1944. Largescale Superficial Structures in the Northampton Ironstone Field. Quart. Journ. Geol. Soc., vol, c. ORWIN, C. S. 1938. The Open Fields.
148
G. BOMFORD
APPENDIX
NEW SECTIONS IN THE INFERIOR OOLITE By G. BOMFORD SMALL PIT N.E. OF LODER'S CROSS (30/505929) P. parkinsoni zone S. truellei subzone (7) 6. Flaggy limestone, passing up into subsoil. Procerites 7 sp. O' Terebratula " sphaeroidalis Seen to about G. garantiana subzone
ft. ins. 2
0
0
5
0
4
0
6
0
8
0 1
8 0
2
0 6
OBLIQUA BED Sb. Oolitic limestone. Parkinsonia sp., Prorsisphinctes miseres (large and common), Leptosphinctes subdivisus, Garantiana garantiana, Oppelia subradiata, O. pleurifera, Lissoceras sp., Sphaeroceras sp., belemnites, Amphitrochilia duplicata, Pictavia bajocensis, Pleurotomaria palaemon, P. bessina, Astarte obliqua, Trigonia costata, T. sp., Goniothyrls phillipsi, O' Terebratula" decipiens 7, .. Rhynchonella " sp,
Sa. Shell conglomerate. Prorsisphinctes miseres, Garantiana garantiana (common), G. aff. althoffi 7, Oppelia pulchra Stephanoceras sp., Poecilimorphus sp., Spiroceras toxoconicum, S. wattoni, Pictavia bajocensis, Pleurotomaria palaemon, Ataphrus sp., Cerithium" sp., Pseudomelania sp., Astarte obliqua, A. sp., Cucullaea cf. oblonga, Nucula sp., Entolium sp., O'
Goniomya literata, Coelopis lunulata, O' Terebratula " decipiens, Ptychothyris stephani, Pygorhytis ringens.i,
Planed surface S. humphriesianum zone 4. Teloceras found in a soft matrix in a hollow in the top of Bed 3b S. sowerbyi (and O. sauzei 7) zone RED BED 3b. Limestone with small red ooliths. Few fossils 3a. Limestone with large red ooliths and numerous snuffboxes," passing down into conglomerate. Hyperlioceras sp., Graphoceras 7 sp., Emarginula 7 sp, attached to bed below, Rhynchonella " sp, Planed surface L. opalinum zone 2. BLUE BED. Blue grey limestone. Bredya crassornata, B 7 sp., Anco/ioceras sp., Lima hersilia, Ceratomya bajociana 1. Sandy grey limestone. Leioceras sp, (7 Cypholioceras) seen to O'
O'
COOMBE QUARRY, NEAR MAPPERTON
(30/496996)
P. parkinsoni zone 6. Oolitic limestone, weathering flaggy, seen to about S. Crinoidal limestone 4. Whitish limestone, much veined with calcite Parkinsonia schloenbachi, P. parkinsoni, Stephanoceras sp., Pictavia bajocensis, Lima sp., Trigonia costata, Pinna sp., Terebratula " sphaeroidalis Planed surface O'
8
149
FIELD MEETING AT WEYMOUTH, DORSET
S. sowerbyi zone 3. Red Bed. Limestone full of large red ooliths. Deltotoceras,
ft. ins.
Hyperlioceras sp., Sonninia sp., .. Cerithium " abbas?, Coelastarte excavata, Gresslya sp, lin. to Planed surface L. murchisonae zone 2. Shell conglomerate. Red ooliths. Ancolioceras sp., ? Brasilia sp., Pseudomelania bicarinata, Pleurotomaria actinomphala, Po elongata*, Gresslya sp., Pleuromya uniformis, Pholadomya jidicula*, .. Terebratula " perovalis, .. Rhynchonella " subangulata, .. Rhynchonella " sp., Montlivaltia 0 to delabechei ... L. opalinum zone l. Grey limestone with scattered yellow ooliths. Leioceras spp., Lytoceras sp., Tmetoceras scissum, Lima hersilia seen to
0
2
0
• Possibly from Bed 30 QUARRY NEAR HORN PARK (31/456020) P. parkinsoni zone 70 Top Beds. Flaggy and rubbly limestone passing up into subsoil. Lissoceras sp., Stephanoceras spp., Parkinsonia aff. schloenbachi sp., P. parkinsonis, Ataphrus laevigatus, Amphitrochilia duplicata, Cucullaea sp., Modiolus sp., Ctenostreon pectiniformis, Coelopis lunulatat; Aulacothyris carinata, .. Terebratula " sphaeroidalis, .. T." eudesi, Ptychothyris stephani, Sphenorhynchia cf. aviformis, Acanthorhynchia panacanthina, Acanthothyris spinosa, Pentacrinus, Cidaris bouchardii, Pygorhytis ringens, Holectypus hemisphericust, Seen Trochocyathus magnevillianus 'l., ° '1 S. sowerbyi or O. sauzei zone 60 Red Bed. Unfossiliferous limestone in two beds. Belemnapsis sp., Lamelliphorus ornatissimus, .. Rhynchonella " sp., Cronoid ossicles ... 5. Clay parting L. murchisonae zone G. concava and B, bradfordensis subzones 4. Limestone with numerous brown ooliths. Graphoceras spp. abundant in the upper part, Brasilia spp. in the lower Lytoceras sp., Tmetoceras sp, juv. aff, scissum S., Brasilia sublineata So, B. ambigua So, B. cf. baylei, B. simi/is So, B. giganteat So, Graphoceras aff, cavatum So, G. aff. pulchra So, G. stigmosum So, G. v-scriptum S., G. aff. concavum* S., G. rudis So, Go (Platygraphoceras) sp. juv., So, Erycites abbas S., Sonninia (Parammatoceras) sp. [uv., S., So (Fissi/obiceras) sp. juv. S., Sonninia spp., Belemnopsis blainvilleit; Amberleya ornata, Procerithium undulatum, Pseudomelania bicarinata, Littorina dorsetensiss, Discohelix altust; Ataphrus laevigatus, Pleurotomaria actinamphala, P. baugieri, P. elongata, P. yeovi/ensis, Amphitrochilia winwoodit, Grammatodon sp., Cucullaea sp.*, Myoconcha crassa, Trigonia bella?, T. costatat, T. striata", Entolium sp., Ctenostreon pectiniformis*, Ostrea sp., Astarte sp.*, Coelastarte excavatat, Trigonastarte trigonalisi, Cardium sp., Nucula? sp., Gresslya peregrina*, Pleuromya uniformls", Pseudoglossothyris ampla, .. Terebratula " eudesi, .. Rhynchonella " subangulata, Cymatorhynchia sp. nov. t Common. • Abundant.
2
8 2
7 1
6
150
FIELD MEETING AT WEYMOUTH, DORSET
B. bradfordensis and L. murchisonae s.s. subzones 3. Grey limestone; ammonites with their chambers generally infilled with crystalline calcite. Tmetoceras sp. juv. aft". scissum S. Ludwigia obtusa" S., L. aft". brasili S., L. obtusiformis S., L. (Welschia) sp., Brasilia bradfordensis S., B. bayleit S., Planammatoceras planiforme S., Pseudomelania bicarinata, Trochus sp., Craterospongia concentrica. * L. murchisonae s.s, and Ancolioceras spp. subzones 2. Yellowish limestone with irregular ochreous patches. Ammonites usually preserved as casts with rotted centres '" Lytoceras (Pachylytoceras) aaleniayum" S., L. (P.) torulosumt S., Ancolioceras substriatum" S., A. costatum" S., Ludwigia obtusa S., L. aft". brasili" S., Ludwigia sp. nov. S., Brasilia sp. S., B. (" Manselia ") cf. subacuta S., " Hammatoceras" sp, S., Nautilust sp., Megateuthis giganteus, Pseudomelania sp., Natica sp. 1, Cucul/aea sp., Modiolus plicatus, Myoconcha crassa", Trigonia striata, Entolium cf. demissum", Chlamys sp, 1, Velata tuberculosa, Lima bradfordensis, L. aft". placida, L. hersilia*, Ctenostreon pectiniformis, Ostrea sp., Lopha sp., Pteroperna sp., Pinna sp., Astarte sp., Trigonastarte trigonalirt; Pseudisocardia cordata, Ceratomya bajocianat, Gresslya peregrina *, Pleuromya uniformis", Pholadomya fidicula"; " Terebratula " perovalist ; Lophrothyris etheridgii, Cincta anglica, Acanthorhynchia panacanthina, "Rhynchonel/a" spp., Discina sp., Palaeopagurus, Apiocrinus, Galeropygus agariciformis, Montlivaltia delabecheit, ? L. opalinum zone 1. Hard crystalline limestone. Many lamellibranchs and some ammonites (Leioceras), but this bed has not long been in Seen to work, and has not yet been collected
ft. ins. 2
0
2
0
0
* Abundant. t Common. Identifications by Dr. L. F. Spath are marked" S." Mr. R. V. Melville has helped with the identification of others.