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Field Meeting in the Oligocene of North-West Isle of Wight
Field Meeting in the Oligocene of North-West Isle of Wight 21·3 June 1963
Report by the Director: F . C. STINTON Received 10 July 1963
members assembled at Yarmouth, Isle of Wight, on the evening of 21 June and after dinner the Director gave a short resume of the programme proposed for the following two days. Visits would be made to see the highest strata of the Oligocene Formation occurring in this country ranging from the Lattorfian Bembridge Limestone up to the Rupelian Upper Hamstead (or Hempstead of early authors) Beds. A warning of the somewhat difficult terrain which would be encountered was given, which perhaps had prevented earlier visits being made by the Association.
THE PARTY OF NINETEEN
Saturday, 22 June The party left Yarmouth by coach after being joined by a group from the Isle of Wight Natural History Society, bringing total numbers to twenty-six. The first stop was at Tapnell, a quarry in the Bembridge Limestone. The section here shows an uppermost layer of limestone fragments in a brownish sandy clay underlaid by thick, very hard travertinous limestone all of which were deposited in lacustrine conditions. From this vantage point which occupies the crest of a hill, the Director described the relation of the outcrop to those on Headon Hill and Whitecliff Bay from which general line the limestone slopes to sea-level at points along the northern seaboard of the Island . The occurrence of giant landsnails was mentioned and a search of the exposure quickly produced many fine specimens of the freshwater snails Limnaea longiscata Brongniart, Planorbis spp. and Viviparus angulosus J. Sowerby, It was noted that the specimens occurred mainly as casts or the original shell structure had been replaced by calcite. Several interesting geodes were found, showing interesting light and dark concentric crystalline bands with fine calcite crystals at their centres, invoking an interesting discussion of the possible mode of their formation. A move was then made for a second exposure of the Bembridge Limestone in another quarry at Prospect, about three-quarters of a mile northeast of the first one. This pit is visible from the main Calbourne road and 87
88
F. C. STINTON
has often been confused with Tapnell. The section here is more complete as the quarry is being extensively worked for road metal and other uses. It is excavated almost to the base of the limestone and a clear vertical face was seen. Lacustrine shells again occur in profusion and a few of the giant land-snails were also obtained. After lunch at Shalfleet the coach proceeded to Gumard where everyone descended to the shore. Throughout this area the cliffs consist of a series of tumbled ledges which are more or less covered with vegetation often nearly to sea-level. At the point of descent, only the Bembridge Limestone was accessible and here the top band of limestone occupied the base of the cliff while the lower bands formed the foreshore. A little to the west, the lower limestone runs out to sea to form Gumard Ledge and at this point a section of the Bembridge Marls overlying the Limestone was seen in the lower cliff. The highest part of the cliff in the immediate area includes some of the Hamstead series but no clear exposures were accessible during this visit. The Director explained the character of the Marls overlying the Limestone at this point and the following section was seen: ft. in. 1. Blue clay containing oysters, Cyrena, Cerithium and Melanoides (Melania) seen immediately belowthe lowestovergrown ledge
2. Pale blue fine-grained limestone (Insect limestone) 3. Dark shaly clay with same fossils as above 4. Oyster Bed with profuse Cyrena, Cerithium mutabile Morris formingthe base of the Bembridge Marls 5. Highestbed of Bembridge Limestone 6. Band of sandy greenish-grey clay with Cyrena and Melanoides (Tarebia) acuta J. Sow., (Melania acuta and M. muricata Forbes) 7. Thick band of tough carbonaceous clay with Viviparus and
o 3
6 0
o
3
Planorbis 8. Green compact clay with few fossils
9. Bembridge Limestoneon foreshore (Gurnard Ledge) It was explained that the occurrence of the clay beds between the limestone bands was a local feature only, probably connected with a lower concentration of calcareous matter in this region at the time of deposition. The Insect limestone, which is septarian in character, produced after a diligent search, several good specimens of elytrae, showing that it was still productive. This section was traced continuously into Thorness Bay until obliterated by a large founder several hundred yards southwards. Immediately beyond this point the highest band of the Bembridge Limestone could be seen running out to sea to form Sticelet Ledge, as the tide had now ebbed. Beyond this point cliff sections were obscure but indurated shell seams which had broken up into curious rectangular blocks formed the foreshore. Beyond this point little of interest was seen until, towards the southern
FIELD MEETING IN THE ISLE OF WIGHT
89
end of the Bay where the land starts to rise again, a well-marked fault was seen, commencing in the low cliff and running across the foreshore out to sea. Extensive indurated limestone bands studded with Cyrena and Melanoides occupied the foreshore, and at Thorness Point a very clear section commencing at about 30 ft. above the shore, immediately below the lowest vegetation-covered ledge, showed the following descending series in the middle of the Bembridge Marls: ft. in. 1. Shaly, ferruginous grey-green clay seen to the vegetation covering 3 0 2. Prominent band of Corbicula obovata J. Sow. 3. Shaly greenish-grey clay with seams of shells 3 0 4. Band of Melanoides ... 0 2 5. Clay parting .,. 0 2 6. Band of Melanoides with numerous seeds, and fish otoliths 0 2 7. Grey clays with seams of Cyrena and Melanopsis carinata J. Sow., this latter fossil forming a thin layer at the base of this bed 2 0 8. Compact green clay with seams of Viviparus 1 2 9. Hard white band of Potamaclis turritissima Forbes and Cyrena. 0 8 This is the lowest bed in the cliff and passes down into 0 3 10. Black stone band of P. turritissima Forbes ... 2 11. Green clay 0 12. Stone band full of Polymesoda convexa Brongniart (= Cyrena 0 2 semistriata Deshayes)... 0 °t 13. Stone band of Melanoides ... 14. Hard stone band with fucoidal markings. This evidently represented a mud layer which had dried out, cracked and the resulting seams had become infiltrated with a fine-grained mud, the whole later hardening into a limestone which overlays a softer 1 in. clayey limestone packed with valves of Polymesoda convexa Brongniart o It 15. Layer of shaly grey clay with numerous valves of Mya and Modiola o 2 with a crushed layer of these shells and Cyrena at the base 16. Shaly green clay with Cyrena throughout and irregular concentra2 6 tions of Viviparus towards the top of the bed 17. Band of shaly grey clay with a prominent t in. seam ofsmall Cyrena and a small Corbicula, often with both valves united o It 18. Soft, greenish limestone with numerous Polymesoda convexa Brongn., the lowest bed seen at low tide The variable fluvio-marine and lacustrine characters of the different layers, indicating varying saline concentrations, were shown by the molluscan contents of the succeeding strata. The party then rejoined the coach and returned to Yarmouth for dinner.
Sunday, 23 June A short coach journey carried members to Cranmore Hill where a short walk brought everyone to the cliff edge. At this point the cliff is some 170 ft. high and is entirely made up of the Hamstead series. The Director explained the nature of the series, consisting of an Upper Marine group, a
90
F. C. STINTON
Middle Freshwater Series and a Lower Estuarine Series underlain by a freshwater bed. In this area the cliffs are again very tumbled and clear sections are infrequent. However, the Upper Marine Series were completely exposed and the following sequence was seen commencing immediately below the cliff top: ft. in. 1. Band of comminuted Cyrenae with Modiola and fish otoliths in an
orange sandy clay 2. Compact bluish-green clay with Ostrea calli/era Lamarck... 3. Prominent ferruginous band packed with broken Polymesoda convexa Brongn., but including whole valves, Pirenella monilifer Defrance (= Cerithium plicatum Lamarck) and Tympanotonos labyrinthus Duchatel (= Cerithium elegans Deshayes) 4. Stiff shaly blue clay with numerous Corbula pisum J. Sow., and Corbula vectensis Forbes, the latter shell becoming very common in the lower part of the bed where the clay becomes darker. There is a prominent band of large, flattened septaria in the centre
0 11
2 0
0
5
7
6
Below this bed the section was obscured by talus and the whole lower part of the cliff is obscured by a great founder which took place many years ago. Many of the characteristic shells were gathered from these slopes including two examples of the volute Athleta rathieri Hebert, which occurs only in the Corbula vectensis Bed. Moving northwards about 100 yards, another section similar to the first was seen but, in addition, the middle freshwater beds were seen at about mid-level of the cliffs. These were found to consist of greyish-green sandy clay with Viviparus above a layer of ferruginous concretions with Unio, below which was a hard, light grey clay with numerous plant remains compressed in very thin seams of sand. After further collecting, lunch was taken on the cliff-top and a vote of thanks was given to the Director. The public footpath to Hamstead was then taken and the shore was reached just west of the Bembridge Limestone forming Hamstead Ledge. Unfortunately, owing to a strong wind, the tide was late in ebbing so that it was impossible to see the Bembridge Marls which occupy the foreshore, but the 'Black Band' forming the base of the Hamstead series was seen in situ about four feet above the shore. Working along the shore towards Bouldner many fragments of chelonian scutes were found amongst the shingle, together with a fine tooth of Diplocynodon hantoniensis Owen, but mammalian remains were scanty, consisting mainly of rolled bones apart from a fine premolar of Palaeotherium which was found a short distance east of Bouldner. Here, also, the Middle Freshwater Beds of the Hampstead series were seen in situ on the foreshore and the beach was littered with large iron-stained septaria, many of them covered with fine examples of Unio.
FIELD MEETING IN THE ISLE OF WIGHT
91
Yarmouth was reached at 6.30 p.m, and the remaining members of the party then dispersed. REFERENCES BRISTOW, H. W., C. REID & A. STRAHAN. 1889. The Geology of the Isle of Wight. 2nd. edn . Mem. geo/. Surv. U.K. British Caenozoic Fossils. Brit. Mus . (Nat. Hist.). 1959. FORBES, E. 1856. On the Tertiary Fluvio-Marine Formation of the Isle of Wight. Mem. geo/. Surv. U.K. JACKSON, J. F. 1925. Notes on Fossiliferous Clays in the Bembridge Limestone near Gurnard, Isle of Wight. Proc. Is. Wight nat. Hist, Soc.,t, 374-7 . MOORMAN, R. F. 1938. Notes on the Fossil Vertebrates of the Hamstead Beds. Proc. Is. Wight nat. Hist, Soc., 3,81-5 WHITE, H . J. OSBORNE. 1921. A Short Account of the Geology of the Isle of Wight. Mem. geol. Surv. U.K. MAPS Sheet 330, Geological Survey. I mile to I inch. Parts of New Forest and the Isle of Wight. Special Sheet. Isle of Wight and Part of Mainland. Geological Survey.
Report by the Director: F . C. STINTON Received 10 July 1963
members assembled at Yarmouth, Isle of Wight, on the evening of 21 June and after dinner the Director gave a short resume of the programme proposed for the following two days. Visits would be made to see the highest strata of the Oligocene Formation occurring in this country ranging from the Lattorfian Bembridge Limestone up to the Rupelian Upper Hamstead (or Hempstead of early authors) Beds. A warning of the somewhat difficult terrain which would be encountered was given, which perhaps had prevented earlier visits being made by the Association.
THE PARTY OF NINETEEN
Saturday, 22 June The party left Yarmouth by coach after being joined by a group from the Isle of Wight Natural History Society, bringing total numbers to twenty-six. The first stop was at Tapnell, a quarry in the Bembridge Limestone. The section here shows an uppermost layer of limestone fragments in a brownish sandy clay underlaid by thick, very hard travertinous limestone all of which were deposited in lacustrine conditions. From this vantage point which occupies the crest of a hill, the Director described the relation of the outcrop to those on Headon Hill and Whitecliff Bay from which general line the limestone slopes to sea-level at points along the northern seaboard of the Island . The occurrence of giant landsnails was mentioned and a search of the exposure quickly produced many fine specimens of the freshwater snails Limnaea longiscata Brongniart, Planorbis spp. and Viviparus angulosus J. Sowerby, It was noted that the specimens occurred mainly as casts or the original shell structure had been replaced by calcite. Several interesting geodes were found, showing interesting light and dark concentric crystalline bands with fine calcite crystals at their centres, invoking an interesting discussion of the possible mode of their formation. A move was then made for a second exposure of the Bembridge Limestone in another quarry at Prospect, about three-quarters of a mile northeast of the first one. This pit is visible from the main Calbourne road and 87
88
F. C. STINTON
has often been confused with Tapnell. The section here is more complete as the quarry is being extensively worked for road metal and other uses. It is excavated almost to the base of the limestone and a clear vertical face was seen. Lacustrine shells again occur in profusion and a few of the giant land-snails were also obtained. After lunch at Shalfleet the coach proceeded to Gumard where everyone descended to the shore. Throughout this area the cliffs consist of a series of tumbled ledges which are more or less covered with vegetation often nearly to sea-level. At the point of descent, only the Bembridge Limestone was accessible and here the top band of limestone occupied the base of the cliff while the lower bands formed the foreshore. A little to the west, the lower limestone runs out to sea to form Gumard Ledge and at this point a section of the Bembridge Marls overlying the Limestone was seen in the lower cliff. The highest part of the cliff in the immediate area includes some of the Hamstead series but no clear exposures were accessible during this visit. The Director explained the character of the Marls overlying the Limestone at this point and the following section was seen: ft. in. 1. Blue clay containing oysters, Cyrena, Cerithium and Melanoides (Melania) seen immediately belowthe lowestovergrown ledge
2. Pale blue fine-grained limestone (Insect limestone) 3. Dark shaly clay with same fossils as above 4. Oyster Bed with profuse Cyrena, Cerithium mutabile Morris formingthe base of the Bembridge Marls 5. Highestbed of Bembridge Limestone 6. Band of sandy greenish-grey clay with Cyrena and Melanoides (Tarebia) acuta J. Sow., (Melania acuta and M. muricata Forbes) 7. Thick band of tough carbonaceous clay with Viviparus and
o 3
6 0
o
3
Planorbis 8. Green compact clay with few fossils
9. Bembridge Limestoneon foreshore (Gurnard Ledge) It was explained that the occurrence of the clay beds between the limestone bands was a local feature only, probably connected with a lower concentration of calcareous matter in this region at the time of deposition. The Insect limestone, which is septarian in character, produced after a diligent search, several good specimens of elytrae, showing that it was still productive. This section was traced continuously into Thorness Bay until obliterated by a large founder several hundred yards southwards. Immediately beyond this point the highest band of the Bembridge Limestone could be seen running out to sea to form Sticelet Ledge, as the tide had now ebbed. Beyond this point cliff sections were obscure but indurated shell seams which had broken up into curious rectangular blocks formed the foreshore. Beyond this point little of interest was seen until, towards the southern
FIELD MEETING IN THE ISLE OF WIGHT
89
end of the Bay where the land starts to rise again, a well-marked fault was seen, commencing in the low cliff and running across the foreshore out to sea. Extensive indurated limestone bands studded with Cyrena and Melanoides occupied the foreshore, and at Thorness Point a very clear section commencing at about 30 ft. above the shore, immediately below the lowest vegetation-covered ledge, showed the following descending series in the middle of the Bembridge Marls: ft. in. 1. Shaly, ferruginous grey-green clay seen to the vegetation covering 3 0 2. Prominent band of Corbicula obovata J. Sow. 3. Shaly greenish-grey clay with seams of shells 3 0 4. Band of Melanoides ... 0 2 5. Clay parting .,. 0 2 6. Band of Melanoides with numerous seeds, and fish otoliths 0 2 7. Grey clays with seams of Cyrena and Melanopsis carinata J. Sow., this latter fossil forming a thin layer at the base of this bed 2 0 8. Compact green clay with seams of Viviparus 1 2 9. Hard white band of Potamaclis turritissima Forbes and Cyrena. 0 8 This is the lowest bed in the cliff and passes down into 0 3 10. Black stone band of P. turritissima Forbes ... 2 11. Green clay 0 12. Stone band full of Polymesoda convexa Brongniart (= Cyrena 0 2 semistriata Deshayes)... 0 °t 13. Stone band of Melanoides ... 14. Hard stone band with fucoidal markings. This evidently represented a mud layer which had dried out, cracked and the resulting seams had become infiltrated with a fine-grained mud, the whole later hardening into a limestone which overlays a softer 1 in. clayey limestone packed with valves of Polymesoda convexa Brongniart o It 15. Layer of shaly grey clay with numerous valves of Mya and Modiola o 2 with a crushed layer of these shells and Cyrena at the base 16. Shaly green clay with Cyrena throughout and irregular concentra2 6 tions of Viviparus towards the top of the bed 17. Band of shaly grey clay with a prominent t in. seam ofsmall Cyrena and a small Corbicula, often with both valves united o It 18. Soft, greenish limestone with numerous Polymesoda convexa Brongn., the lowest bed seen at low tide The variable fluvio-marine and lacustrine characters of the different layers, indicating varying saline concentrations, were shown by the molluscan contents of the succeeding strata. The party then rejoined the coach and returned to Yarmouth for dinner.
Sunday, 23 June A short coach journey carried members to Cranmore Hill where a short walk brought everyone to the cliff edge. At this point the cliff is some 170 ft. high and is entirely made up of the Hamstead series. The Director explained the nature of the series, consisting of an Upper Marine group, a
90
F. C. STINTON
Middle Freshwater Series and a Lower Estuarine Series underlain by a freshwater bed. In this area the cliffs are again very tumbled and clear sections are infrequent. However, the Upper Marine Series were completely exposed and the following sequence was seen commencing immediately below the cliff top: ft. in. 1. Band of comminuted Cyrenae with Modiola and fish otoliths in an
orange sandy clay 2. Compact bluish-green clay with Ostrea calli/era Lamarck... 3. Prominent ferruginous band packed with broken Polymesoda convexa Brongn., but including whole valves, Pirenella monilifer Defrance (= Cerithium plicatum Lamarck) and Tympanotonos labyrinthus Duchatel (= Cerithium elegans Deshayes) 4. Stiff shaly blue clay with numerous Corbula pisum J. Sow., and Corbula vectensis Forbes, the latter shell becoming very common in the lower part of the bed where the clay becomes darker. There is a prominent band of large, flattened septaria in the centre
0 11
2 0
0
5
7
6
Below this bed the section was obscured by talus and the whole lower part of the cliff is obscured by a great founder which took place many years ago. Many of the characteristic shells were gathered from these slopes including two examples of the volute Athleta rathieri Hebert, which occurs only in the Corbula vectensis Bed. Moving northwards about 100 yards, another section similar to the first was seen but, in addition, the middle freshwater beds were seen at about mid-level of the cliffs. These were found to consist of greyish-green sandy clay with Viviparus above a layer of ferruginous concretions with Unio, below which was a hard, light grey clay with numerous plant remains compressed in very thin seams of sand. After further collecting, lunch was taken on the cliff-top and a vote of thanks was given to the Director. The public footpath to Hamstead was then taken and the shore was reached just west of the Bembridge Limestone forming Hamstead Ledge. Unfortunately, owing to a strong wind, the tide was late in ebbing so that it was impossible to see the Bembridge Marls which occupy the foreshore, but the 'Black Band' forming the base of the Hamstead series was seen in situ about four feet above the shore. Working along the shore towards Bouldner many fragments of chelonian scutes were found amongst the shingle, together with a fine tooth of Diplocynodon hantoniensis Owen, but mammalian remains were scanty, consisting mainly of rolled bones apart from a fine premolar of Palaeotherium which was found a short distance east of Bouldner. Here, also, the Middle Freshwater Beds of the Hampstead series were seen in situ on the foreshore and the beach was littered with large iron-stained septaria, many of them covered with fine examples of Unio.
FIELD MEETING IN THE ISLE OF WIGHT
91
Yarmouth was reached at 6.30 p.m, and the remaining members of the party then dispersed. REFERENCES BRISTOW, H. W., C. REID & A. STRAHAN. 1889. The Geology of the Isle of Wight. 2nd. edn . Mem. geo/. Surv. U.K. British Caenozoic Fossils. Brit. Mus . (Nat. Hist.). 1959. FORBES, E. 1856. On the Tertiary Fluvio-Marine Formation of the Isle of Wight. Mem. geo/. Surv. U.K. JACKSON, J. F. 1925. Notes on Fossiliferous Clays in the Bembridge Limestone near Gurnard, Isle of Wight. Proc. Is. Wight nat. Hist, Soc.,t, 374-7 . MOORMAN, R. F. 1938. Notes on the Fossil Vertebrates of the Hamstead Beds. Proc. Is. Wight nat. Hist, Soc., 3,81-5 WHITE, H . J. OSBORNE. 1921. A Short Account of the Geology of the Isle of Wight. Mem. geol. Surv. U.K. MAPS Sheet 330, Geological Survey. I mile to I inch. Parts of New Forest and the Isle of Wight. Special Sheet. Isle of Wight and Part of Mainland. Geological Survey.