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Whitsun field meeting report: Devonian of Torbay
Whitsun Field Meeting Report: Devonian of Torbay 8-11 June 1962
Report by the Director: G. F. ELLIOTT Received 24 November 1962
assembled at the Party Headquarters, King's Ash Hill Holiday Camp, Paignton, on the Friday evening, when the Director spoke of the programme to be followed, and of the marine Devonian and its correlation with that of other areas, notably the German Rhineland and Belgian Ardennes, where the succession of faunas and facies are much better displayed than in the tectonically disturbed type-Devonian, permitting reconstructions such as those of Lecompte (1959). Although the general dip in the Torbay area is to the north, Lower Middle and Upper Devonian occur in varying associations at or near the southern, central and northern Torbay coasts, and it was emphasised that many details of structure await elucidation. The party would visit most of the local fossillocalities, and would at the same time examine all other adjacent exposures. Seven other members, mostly resident in the district,' joined for the subsequent field trips. FIFTEEN MEMBERS
9 June 1962 The party proceeded by coach to the quarries at Lummaton Hill. At the entrance to the workings a short account of the history of palaeontological investigations at this classic Middle Devonian locality was given. Members were reminded that Phillip's pioneer account of Devonian fossils (1841) contains many Lummaton species listed as from Torquay or Barton. Later, the Palaeontographical Society monograph of Whidborne (18891907), a local clergyman, was in great part based on Lummaton material, which also figured prominently in Davidson's British Devonian Brachiopod monograph (1864-82). Jukes-Brown (1906) recognised a generalised succession in the massive and thrust limestones seen in the extensive quarries and adjacent former exposures, when traced from south-east to north-west, of probable Couvinian through Givetian to the base of the Frasnian. The extent of Whidborne's fossil-bed and Jukes-Brown's later observations on this were reviewed by Elliott (1961) in fixing the top Middle Devonian age of a new calcareous alga discovered by him in this bed. Members were then welcomed by the quarry Manager, Mr. D. Down, who had generously laid out an interesting collection of fossils revealed during recent quarrying: 81
82
G. F. ELLIOTT
brachiopods, lamellibranchs, crinoids, corals and trilobites; to these the Director added a selection of thin-sections of the shell-band limestone. The quarries were then examined from the southern portion now in work, round to the disused north-western portion; massive dolomitisation, the position of Whidborne's fossil-bed as detailed by Jukes-Brown, and other features were examined as far as possible. Considerable discussion ensued on the nature of the faulting or thrusting in the massive limestones, in which clear bedding planes were not seen. On this and subsequent visits the party were fortunate to be accompanied by Mr. Vachell, who has been mapping the structures of the area; from the high ground above the quarries the party looked northwards to the detached limestone mass of Barton, and Mr. Vachell gave a brief summary of his views of the structure. Walking by road to the small western quarry, the position of another exposure of Whidborne's fossil bed and the technique of collecting from it were demonstrated. The fossil-bed was seen to lie at the very top of the quarry in the central portion of the eastern face, most of the quarry-face below being of massive, largely dolomitised, stromatoporoid limestone. The fossil bed weathers distinctively, and is then easily broken and the fossils cleanly extracted. Recent levelling of the top of the hill as part of the quarry operations has ploughed up much of this bed, but there was plenty of material for examination. The Director explained that the apparent conflict in agesignificance between the Givetian Stringocephalus burtini and the supposed Frasnian Hypothyridina cuboides, which occur together in the main limestones of the other quarries, was due to the confusion of different species under the second name, and that the fossil-bed containing the true (Givetian) H. cuboides may be taken as at or near the top of the Givetian (Elliott, 1961). This brachiopod evidence has since been confirmed by the ammonoid dating (House, 1963). After lunch near by the party proceeded by coach to Ilsham, passing the site of the well-known 'Kent's Cavern' (not visited on this occasion), and then walked to Hope's Nose-Mr. Vachell demonstrating roadside exposures of different Devonian shales en route- and descended to the old quarry. Here the faulted Lower Devonian, and markedly unconformable succession of thin-bedded on thick-bedded Middle Devonian, were clearly seen in spite of much weathering. The Director explained the alternative opinions on this section set out by Lloyd (1933): after a lively discussion, members unanimously agreed that the section showed straightforward contemporaneous erosion and local redeposition. This is the view of Dineley (1961, 134) where Hope's Nose is used as an example for the generalised 'Suggested ecological and depositional zones around the Middle Devonian reefs of Torbay'. After collecting within the quarry, and along the adjacent coast and reefs to the east, where seams of brachiopods were well displayed, members
DEVONIAN OF TORBAY-WHITSUN FIELD MEETING 83
worked their way along to the famous raised beach at the southern end of the peninsula. Although a little awkward of access, this showed a clear section of the component layers, which members were able to sample. An excellent account of this beach and its relation to other, similar, local deposits has recently appeared (Orme, 1960). The party then walked to Meadfoot Bay by Kilmorie Hill, now regrettably subjected to housing development, where local tectonic features were indicated, and after a brief examination of the type Meadfoot Beds, which Mr. Vachell emphasised were to be regarded as a Lower Devonian facies rather than as marking a definite time-interval, went to a very welcome tea and so back to Headquarters by coach. 10 June 1962
Waterside Cove, Goodrington
At the classic site of Waterside Cove, Goodrington, members saw the unconformable New Red Beds resting on Lower Devonian to the north. This is separated by a reversed fault from the Upper Devonian, which begins with purplish mudstones representing the Fammenian. On the south side of the cove these pass down into red mudstones (Frasnian) with large concretions of paler hard calcareous mudstone: this is the well-known goniatite fossil-bed (Lee, 1877; Anniss, 1927) equivalent faunally to the German Biidesheim shales. The bedding is here considered vertical in the Survey account (Lloyd, 1933), and this view is certainly consonant with the thicknesses displayed in this small cove. A dyke-like feature of limestone towards the Fammenian base, vertical in the cliff and running out to sea, was considered a horizon of concretionary limestone (Lloyd, op.cit.y. Mr. Vachell, however, stated that from his local mapping very high dips were unlikely at this point. The discussion which ensued on this point was interesting, but not conclusive. Collecting conditions in the Frasnian Shales were not ideal, but at least one member of the party found a good goniatite. From Waterside the coach took the members to Shoalstone, where the party ascended through the woods to Berry Head Common. At the entrance to the large Berry Head quarries they were met by Mr. Smith, of the Quarry staff, who explained the working of the various levels in a 2oo-foot succession of massive unfossiliferous Middle Devonian limestones and dolomites. This mass of limestone, its age Givetian from the evidence of the coast-section to the south, is penetrated by large pipes filled with New Red from the plateau above. Some of these had been revealed by quarrying operations. Solution caves with stalactites are sometimes broken into, and one of these, only recently revealed by current work, attracted much attention. Good specimens of calcite crystals and dolomite concretions were collected: the chemistry of the latter was discussed.
84
G. F. ELLIOTT
Lunch was taken on the slopes by the southern fort south of Berry Head, a survival from the invasion threat of the Napoleonic Wars. The Director spoke briefly of the geological dating of the plateau, here better seen than to the north of Torbay. Various Mesozoic and Tertiary dates have been suggested for this probable marine planation, though the Pliocene, well developed elsewhere in Britain, is discounted (see summary in Lloyd, 1933). The remains of New Red deposits on the plateau suggest that the smoothing may have begun as early as the Permian. Attention was drawn to the curious mixture of calcicole and calcifuge plants, a reflection of the varied patchy soils formed from the underlying limestone and sandstone. Some of the party then followed the Director in a steep cliff descent to thin-bedded limestones about 120-130 feet below the fort and twenty to thirty feet above mean sea level (Nat. Grid. 943561). These limestones, of which ten to twenty feet are well exposed, are fossiliferous, with crinoids, stromatoporoids and occasional corals, but have not yet been accurately dated. Seen from the sea, the dips suggest that they are at a lower level than the base of the 200 feet seen in the Berry Head Quarries. They are not lithologically typical Couvinian limestones as seen farther to the south, and may be approximately at the Couvinian-Givetian junction level of the Middle Devonian. In thin-section they show red and grey sparry limestones with crinoid remains predominating. The coach then took members to a tea-break in Brixham, then to Mudstone Bay. Here the well-known anticline of Couvinian shales, overlain north and south by dark thin-bedded shaly Couvinian limestones, was studied. The shales, micaceous and sometimes papery, with calcareous and siliceous veins, represent a deeper-water muddy facies and have been known since the days of Phillips for their cephalopod fauna. On this occasion extensive hammering by the party failed to produce more than a few good corals and poor brachiopod impressions.
11 June 1962 On Monday the members went by coach to Broadsands and walked to Elberry Cove, for the examination of the complicated and far from clear relations of red Upper Devonian and grey Middle Devonian. Dividing into three, the party examined the jointed rocks and reefs to the north, some of which yielded Middle Devonian corals; the overgrown Upper Devonian mudstones at the back of the cove, with Mr. Vachell; and the red shales and limestones apparently underlying the Middle Devonian to the east of the cove, with the Director. Further work along the coast was prevented by the state of the tide. The party then went to Brixham, and ascended to Windmill Hill, to the entrance to the celebrated cavern. The Director spoke of the significance in
DEVONIAN OF TORBAY-WHITSUN FIELD MEETING 85
British palaeolithic studies of this cave, discovered in 1858, and with the excavation with which the names of Pengelly and Prestwich are associated. Although entry to the cave is by payment, it is a pleasure to report that it is little commercialised in the popular sense of the word. Lunch was taken in Brixham and votes of thanks to the Director, to Mr. B. Ainsley who had acted as Excursion Secretary, and to Mr. Vachell, were proposed; the party then returned to Paignton and dispersed. Most of the programme was carried out in hot bright sunshine, and rain on Monday did not seriously interfere with the work. Thanks are due to Teign Valley Granite Co. Ltd. and RC.C. Quarries Ltd. for permission to visit the Lummaton and Brixham Quarries respectively.
REFERENCES ANNISS, L. G. 1927. The Geology of the Saltern Cove Area, Torbay. Quart. J. geol. Soc. Lond., 83, 492-500. DAVIDSON, T. 1864--82. A Monograph of British Devonian Brachiopoda. Palaeontogr. Soc. [Monogr.). DINELEY, D. L. 1961. The Devonian System in South Devonshire. Field Studies, 1 (3), 121--40. ELLIOTT, G. F. 1961. A New British Devonian Alga, Palaeoporella lummatonensis, and the Brachiopod Evidence of the Age of the Lummaton Shell-Bed. Proc. Geol. Ass., Lond., 72,251-60. HOUSE, M. R. 1963. Devonian Ammonoid Successions and Facies in Devon and Cornwall. Quart J. geol. Soc. Lond., 119, 1-27. JUKES-BROWN, A. J. 1906. The Devonian Limestones of Lummaton Hill, near Torquay. Proc. Geol. Ass., Lond., 19,291-302. LECOMPTE, M. i959. Le phenomene calcaire devonien dans Ie geosynclinal belgorhenan: sa genese, ses enseignements, ses problems. Rev. Quest. Sci., 321-54. LEE, J. E. 1877. Notice of the Discovery of Upper Devonian Fossils in the Shales of Torbay. Geol. Mag., 4, 100-2. LLOYD, W. 1933. The Geology of the Country around Torquay. 2nd ed. (revised). Mem. geol. Surv. U. K. ORME, A. R. 1960. The Raised Beaches and Strandlines of South Devon. Field Studies, 1 (2), 109-30. PmLLIPs, J. 1841. Figures and Descriptions of the Palaeozoic Fossils of Cornwall, Devon and West Somerset. iGeol. Surv.), London. WHIDBORNE, G. F. 1889-1097. A Monograph of the Devonian Fauna of the South of England. Palaeontogr, Soc. [Monogr.).
Report by the Director: G. F. ELLIOTT Received 24 November 1962
assembled at the Party Headquarters, King's Ash Hill Holiday Camp, Paignton, on the Friday evening, when the Director spoke of the programme to be followed, and of the marine Devonian and its correlation with that of other areas, notably the German Rhineland and Belgian Ardennes, where the succession of faunas and facies are much better displayed than in the tectonically disturbed type-Devonian, permitting reconstructions such as those of Lecompte (1959). Although the general dip in the Torbay area is to the north, Lower Middle and Upper Devonian occur in varying associations at or near the southern, central and northern Torbay coasts, and it was emphasised that many details of structure await elucidation. The party would visit most of the local fossillocalities, and would at the same time examine all other adjacent exposures. Seven other members, mostly resident in the district,' joined for the subsequent field trips. FIFTEEN MEMBERS
9 June 1962 The party proceeded by coach to the quarries at Lummaton Hill. At the entrance to the workings a short account of the history of palaeontological investigations at this classic Middle Devonian locality was given. Members were reminded that Phillip's pioneer account of Devonian fossils (1841) contains many Lummaton species listed as from Torquay or Barton. Later, the Palaeontographical Society monograph of Whidborne (18891907), a local clergyman, was in great part based on Lummaton material, which also figured prominently in Davidson's British Devonian Brachiopod monograph (1864-82). Jukes-Brown (1906) recognised a generalised succession in the massive and thrust limestones seen in the extensive quarries and adjacent former exposures, when traced from south-east to north-west, of probable Couvinian through Givetian to the base of the Frasnian. The extent of Whidborne's fossil-bed and Jukes-Brown's later observations on this were reviewed by Elliott (1961) in fixing the top Middle Devonian age of a new calcareous alga discovered by him in this bed. Members were then welcomed by the quarry Manager, Mr. D. Down, who had generously laid out an interesting collection of fossils revealed during recent quarrying: 81
82
G. F. ELLIOTT
brachiopods, lamellibranchs, crinoids, corals and trilobites; to these the Director added a selection of thin-sections of the shell-band limestone. The quarries were then examined from the southern portion now in work, round to the disused north-western portion; massive dolomitisation, the position of Whidborne's fossil-bed as detailed by Jukes-Brown, and other features were examined as far as possible. Considerable discussion ensued on the nature of the faulting or thrusting in the massive limestones, in which clear bedding planes were not seen. On this and subsequent visits the party were fortunate to be accompanied by Mr. Vachell, who has been mapping the structures of the area; from the high ground above the quarries the party looked northwards to the detached limestone mass of Barton, and Mr. Vachell gave a brief summary of his views of the structure. Walking by road to the small western quarry, the position of another exposure of Whidborne's fossil bed and the technique of collecting from it were demonstrated. The fossil-bed was seen to lie at the very top of the quarry in the central portion of the eastern face, most of the quarry-face below being of massive, largely dolomitised, stromatoporoid limestone. The fossil bed weathers distinctively, and is then easily broken and the fossils cleanly extracted. Recent levelling of the top of the hill as part of the quarry operations has ploughed up much of this bed, but there was plenty of material for examination. The Director explained that the apparent conflict in agesignificance between the Givetian Stringocephalus burtini and the supposed Frasnian Hypothyridina cuboides, which occur together in the main limestones of the other quarries, was due to the confusion of different species under the second name, and that the fossil-bed containing the true (Givetian) H. cuboides may be taken as at or near the top of the Givetian (Elliott, 1961). This brachiopod evidence has since been confirmed by the ammonoid dating (House, 1963). After lunch near by the party proceeded by coach to Ilsham, passing the site of the well-known 'Kent's Cavern' (not visited on this occasion), and then walked to Hope's Nose-Mr. Vachell demonstrating roadside exposures of different Devonian shales en route- and descended to the old quarry. Here the faulted Lower Devonian, and markedly unconformable succession of thin-bedded on thick-bedded Middle Devonian, were clearly seen in spite of much weathering. The Director explained the alternative opinions on this section set out by Lloyd (1933): after a lively discussion, members unanimously agreed that the section showed straightforward contemporaneous erosion and local redeposition. This is the view of Dineley (1961, 134) where Hope's Nose is used as an example for the generalised 'Suggested ecological and depositional zones around the Middle Devonian reefs of Torbay'. After collecting within the quarry, and along the adjacent coast and reefs to the east, where seams of brachiopods were well displayed, members
DEVONIAN OF TORBAY-WHITSUN FIELD MEETING 83
worked their way along to the famous raised beach at the southern end of the peninsula. Although a little awkward of access, this showed a clear section of the component layers, which members were able to sample. An excellent account of this beach and its relation to other, similar, local deposits has recently appeared (Orme, 1960). The party then walked to Meadfoot Bay by Kilmorie Hill, now regrettably subjected to housing development, where local tectonic features were indicated, and after a brief examination of the type Meadfoot Beds, which Mr. Vachell emphasised were to be regarded as a Lower Devonian facies rather than as marking a definite time-interval, went to a very welcome tea and so back to Headquarters by coach. 10 June 1962
Waterside Cove, Goodrington
At the classic site of Waterside Cove, Goodrington, members saw the unconformable New Red Beds resting on Lower Devonian to the north. This is separated by a reversed fault from the Upper Devonian, which begins with purplish mudstones representing the Fammenian. On the south side of the cove these pass down into red mudstones (Frasnian) with large concretions of paler hard calcareous mudstone: this is the well-known goniatite fossil-bed (Lee, 1877; Anniss, 1927) equivalent faunally to the German Biidesheim shales. The bedding is here considered vertical in the Survey account (Lloyd, 1933), and this view is certainly consonant with the thicknesses displayed in this small cove. A dyke-like feature of limestone towards the Fammenian base, vertical in the cliff and running out to sea, was considered a horizon of concretionary limestone (Lloyd, op.cit.y. Mr. Vachell, however, stated that from his local mapping very high dips were unlikely at this point. The discussion which ensued on this point was interesting, but not conclusive. Collecting conditions in the Frasnian Shales were not ideal, but at least one member of the party found a good goniatite. From Waterside the coach took the members to Shoalstone, where the party ascended through the woods to Berry Head Common. At the entrance to the large Berry Head quarries they were met by Mr. Smith, of the Quarry staff, who explained the working of the various levels in a 2oo-foot succession of massive unfossiliferous Middle Devonian limestones and dolomites. This mass of limestone, its age Givetian from the evidence of the coast-section to the south, is penetrated by large pipes filled with New Red from the plateau above. Some of these had been revealed by quarrying operations. Solution caves with stalactites are sometimes broken into, and one of these, only recently revealed by current work, attracted much attention. Good specimens of calcite crystals and dolomite concretions were collected: the chemistry of the latter was discussed.
84
G. F. ELLIOTT
Lunch was taken on the slopes by the southern fort south of Berry Head, a survival from the invasion threat of the Napoleonic Wars. The Director spoke briefly of the geological dating of the plateau, here better seen than to the north of Torbay. Various Mesozoic and Tertiary dates have been suggested for this probable marine planation, though the Pliocene, well developed elsewhere in Britain, is discounted (see summary in Lloyd, 1933). The remains of New Red deposits on the plateau suggest that the smoothing may have begun as early as the Permian. Attention was drawn to the curious mixture of calcicole and calcifuge plants, a reflection of the varied patchy soils formed from the underlying limestone and sandstone. Some of the party then followed the Director in a steep cliff descent to thin-bedded limestones about 120-130 feet below the fort and twenty to thirty feet above mean sea level (Nat. Grid. 943561). These limestones, of which ten to twenty feet are well exposed, are fossiliferous, with crinoids, stromatoporoids and occasional corals, but have not yet been accurately dated. Seen from the sea, the dips suggest that they are at a lower level than the base of the 200 feet seen in the Berry Head Quarries. They are not lithologically typical Couvinian limestones as seen farther to the south, and may be approximately at the Couvinian-Givetian junction level of the Middle Devonian. In thin-section they show red and grey sparry limestones with crinoid remains predominating. The coach then took members to a tea-break in Brixham, then to Mudstone Bay. Here the well-known anticline of Couvinian shales, overlain north and south by dark thin-bedded shaly Couvinian limestones, was studied. The shales, micaceous and sometimes papery, with calcareous and siliceous veins, represent a deeper-water muddy facies and have been known since the days of Phillips for their cephalopod fauna. On this occasion extensive hammering by the party failed to produce more than a few good corals and poor brachiopod impressions.
11 June 1962 On Monday the members went by coach to Broadsands and walked to Elberry Cove, for the examination of the complicated and far from clear relations of red Upper Devonian and grey Middle Devonian. Dividing into three, the party examined the jointed rocks and reefs to the north, some of which yielded Middle Devonian corals; the overgrown Upper Devonian mudstones at the back of the cove, with Mr. Vachell; and the red shales and limestones apparently underlying the Middle Devonian to the east of the cove, with the Director. Further work along the coast was prevented by the state of the tide. The party then went to Brixham, and ascended to Windmill Hill, to the entrance to the celebrated cavern. The Director spoke of the significance in
DEVONIAN OF TORBAY-WHITSUN FIELD MEETING 85
British palaeolithic studies of this cave, discovered in 1858, and with the excavation with which the names of Pengelly and Prestwich are associated. Although entry to the cave is by payment, it is a pleasure to report that it is little commercialised in the popular sense of the word. Lunch was taken in Brixham and votes of thanks to the Director, to Mr. B. Ainsley who had acted as Excursion Secretary, and to Mr. Vachell, were proposed; the party then returned to Paignton and dispersed. Most of the programme was carried out in hot bright sunshine, and rain on Monday did not seriously interfere with the work. Thanks are due to Teign Valley Granite Co. Ltd. and RC.C. Quarries Ltd. for permission to visit the Lummaton and Brixham Quarries respectively.
REFERENCES ANNISS, L. G. 1927. The Geology of the Saltern Cove Area, Torbay. Quart. J. geol. Soc. Lond., 83, 492-500. DAVIDSON, T. 1864--82. A Monograph of British Devonian Brachiopoda. Palaeontogr. Soc. [Monogr.). DINELEY, D. L. 1961. The Devonian System in South Devonshire. Field Studies, 1 (3), 121--40. ELLIOTT, G. F. 1961. A New British Devonian Alga, Palaeoporella lummatonensis, and the Brachiopod Evidence of the Age of the Lummaton Shell-Bed. Proc. Geol. Ass., Lond., 72,251-60. HOUSE, M. R. 1963. Devonian Ammonoid Successions and Facies in Devon and Cornwall. Quart J. geol. Soc. Lond., 119, 1-27. JUKES-BROWN, A. J. 1906. The Devonian Limestones of Lummaton Hill, near Torquay. Proc. Geol. Ass., Lond., 19,291-302. LECOMPTE, M. i959. Le phenomene calcaire devonien dans Ie geosynclinal belgorhenan: sa genese, ses enseignements, ses problems. Rev. Quest. Sci., 321-54. LEE, J. E. 1877. Notice of the Discovery of Upper Devonian Fossils in the Shales of Torbay. Geol. Mag., 4, 100-2. LLOYD, W. 1933. The Geology of the Country around Torquay. 2nd ed. (revised). Mem. geol. Surv. U. K. ORME, A. R. 1960. The Raised Beaches and Strandlines of South Devon. Field Studies, 1 (2), 109-30. PmLLIPs, J. 1841. Figures and Descriptions of the Palaeozoic Fossils of Cornwall, Devon and West Somerset. iGeol. Surv.), London. WHIDBORNE, G. F. 1889-1097. A Monograph of the Devonian Fauna of the South of England. Palaeontogr, Soc. [Monogr.).