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Field meeting at Elmstead Woods, Kent
219
FIELD MEETING AT ELMSTEAD WOODS, KENT. Saturday, 28th July, 1944. Report by the Director: Arthur Wrigley. [Received 23rd August, 1945.)
ON this repetition of last year's field meeting at Elmstead Woods,
our seventh visit since 1864, there was no distraction of flying bombs and we appreciated the blessing of peace, but not of plenty, for tea was unobtainable. After a glance at the station cutting where the pebbly Blackheath sands overlie the Woolwich bottom-bed at about rail-level, we ascended the high ground of Elmstead Woods above the railway tunnel. Passing a grotto built of stone from the Rock-pit, an extensive view opened from the northern brow of the hill. Standing on the lowest London Clay, we looked down westward over the slope of Blackheath pebbles to the Woolwich beds and Thanet Sands with a small anticlinal inlier of Chalk on the golf course below. Northward, favoured by clear, sunny weather, was a fine view of London, with St. Paul's dome distinctly seen against the dim outline of the Hampstead ridge, on a horizon 14 miles away. Descending the hill, we soon found the well-known Rock-pit in an enclosed copse hard by the station. Geologists have always called this spot Sundridge Park, for it used to lie within a large estate of that name, but now it seems best to refer it to Elmstead Woods, because the present place and station called Sundridge Park are over a mile away. The fine section of the Rock-pit showed us 20 feet of pebbly sands of the Blackheath beds above an 8 feet talus, and Whitaker records that 15 feet of sand and pebbles have been pierced from the floor of the pit. This total of 43 feet agrees with the 40 feet of Blackheaths observed at the southern end of the neighbouring railway tunnel. The sands were seen to be strongly current bedded, with flint pebbles smaller and sparser than in many other localities. The whole section is crowded with fossils, either whole and very friable, or forming seams of comminuted shells. Only a few species are common, with scattered rarities, and there is a marked contrast with the far more marine fauna which was found in the railway tunnel, perhaps at a slightly lower horizon. This occurrence of the marine, Oldhaven type (tunnel) and the" estuarine" Blackheath type (Rock-pit) in such a limited area, caused Whitaker and Stamp to use both terms in their descriptions of the place. At the top of the section, following the slope of the ground rather than forming a definite horizon, the beds are indurated into a conglomerate of flint pebbles, oyster and " Cyrena" shells, which is the" rock" for which the pit was opened. Unconsolidated beds are seen to pass laterally into the conglomerate. By discussion on the spot we saw that we had before us a
220
A. WRIGLEY,
striking case of the problem of derivative fossils. The large Ostrea bellovacina found here are often bivalve and frequently seen grown to flint pebbles. They could not have travelled far and must have lived in the sea upon a pebbly bottom. This observation on the Rock-pit was clearly made in 1813 by Townsend in his Character oj Moses, and he adds: "There are many single shells which are worm-eaten or covered by Serpulae." These are the " Cyrena" which are so common and which abound in the Woolwich shell-beds below, where they are bivalve. Remembering that the Blackheath beds mark a marine transgression over a lagunar continental margin, it seems highly probable that masses of Woolwich-bed shells were swept into the Blackheath Sea and re-deposited there in these current-bedded sands. Probable derivatives of this kind are marked * in the following list. The previously published faunal lists for " Sundridge Park" combine the Rock-pit and the tunnel' into one locality, so it seems desirable to record what we found in the Rock-pit alone, during our visit or in preparation for it. Fossils of the Blackheath Beds in the Rock-Pit at Elmstead Woods. A-abundant, C-common, R-rare. Obsolete generic names are within square brackets. C. Serpula sp. grown upon" Cyrena." R. Discinisca Jerroviae Muir-Wood, a brachiopod found inside bivalve Ostrea: although it occurs rarely in the Woolwich Beds, its present situation and its great fragility preclude the idea of derivation. R. Nucula fragilis Desh. *R. [Area] Barbatia modioliformis (Desh.), [Pectunculus] Glycymeris plumsteadiensis (J. Sby.). A. Ostrea bellovacina Lam. *R. O. tenera J. Sby., always broken, never bivalve. *A. [Cyrena] Corbicula cuneiformis (J. Sby.), *C. C. cordata (Mor.), usually broken. R. Phacoides 2 spp., minute and bivalve. C. [Corbulomya] Lentidium antiquum (Desh.), bivalve. C. [Corbula] Aloidis arnouldi (Nyst). R. A. morrisi Edw. MS. [=regulbiensis var, B Morris]. R. Theodoxus subornatus (d'Orb.) with colour markings. R. Theodoxus uniplicatus (J. de C. Sby.), * " Hydrobia " parkinsoni Morris R. Melanopsis sp., broken. *C. "Melania" inquinata Defr. *c. Tympanotonus funatus (Mant.). R. Calyptraea sp. . R. Murex abbatiae Wrig. R. Pollia lata (J. Sby.]. *C. "Planorbis" hemistoma J. Sby. 1 Meyer's collection of fossils from the Elmstead Woods railway tunnel is preserved in the Sedgwick Museum, Cambridge, together with his MS. list of them.
PROC. GEOL.
Assoc.,
VOL.
LVI (1945.)
PLATE
9
[Photo: G. Austin Browne.
A.-BLACKHEATH BEDS, WITH SHELLS AND ELMSTEAD WOODS.
PEBBLES;
ROCK-PIT,
[Photo: A. J. Bull. B.-FOSSILIFEROUS BLACKHEATH BEDS; ROCK-PIT, ELMSTEAD WOODS.
[To face p, 220.
FIELD MEETING AT ELMSTEAD WOODS, KENT.
221
The decayed condition of the majority of these mollusca, whose shells are of aragonite, is strongly contrasted with the unaltered calcite of the Ostrea. One sometimes wonders if the unfossiliferous condition of many exposures of Blackheath beds is due to their decalcification, but were this so the oysters, which always are present among the fossils, would surely have remained. Mr. H. W. Harrison kindly permitted us to visit the Rock-pit, Dr. Himus was Field Meeting Secretary, and we are indebted to Dr. A. J. Bull and to Mr. G. Austin Browne for the photographs of this noteworthy section, reproduced on plate 9, which give a general impression of the current bedding and the projecting masses of " rock" in the upper part and adds the detail of a 4-inch band of flint pebbles and fossil shells.
REFERENCES 1811. Organic Remains of a former World, vol. iii, p. 213. TOWNSEND, 1813. The Character of Moses established for Veracity as an historian, pp, 251, 257. BUCKLAND, W. 1817. Trans. Geol. Soc., vol. iv, pp. 277MANTELL, G. A. 1844. Medals of Creation, vol, i, p. 385. WHITAKER, W. 1889. Geology of London, vol. i, p. 227. STAMP, L. D. 1920. Proc. Geol. Assoc., vol. xxxi, pp. 151-3, with further references'. PARKINSON,
J. J.
FIELD MEETING AT ELMSTEAD WOODS, KENT. Saturday, 28th July, 1944. Report by the Director: Arthur Wrigley. [Received 23rd August, 1945.)
ON this repetition of last year's field meeting at Elmstead Woods,
our seventh visit since 1864, there was no distraction of flying bombs and we appreciated the blessing of peace, but not of plenty, for tea was unobtainable. After a glance at the station cutting where the pebbly Blackheath sands overlie the Woolwich bottom-bed at about rail-level, we ascended the high ground of Elmstead Woods above the railway tunnel. Passing a grotto built of stone from the Rock-pit, an extensive view opened from the northern brow of the hill. Standing on the lowest London Clay, we looked down westward over the slope of Blackheath pebbles to the Woolwich beds and Thanet Sands with a small anticlinal inlier of Chalk on the golf course below. Northward, favoured by clear, sunny weather, was a fine view of London, with St. Paul's dome distinctly seen against the dim outline of the Hampstead ridge, on a horizon 14 miles away. Descending the hill, we soon found the well-known Rock-pit in an enclosed copse hard by the station. Geologists have always called this spot Sundridge Park, for it used to lie within a large estate of that name, but now it seems best to refer it to Elmstead Woods, because the present place and station called Sundridge Park are over a mile away. The fine section of the Rock-pit showed us 20 feet of pebbly sands of the Blackheath beds above an 8 feet talus, and Whitaker records that 15 feet of sand and pebbles have been pierced from the floor of the pit. This total of 43 feet agrees with the 40 feet of Blackheaths observed at the southern end of the neighbouring railway tunnel. The sands were seen to be strongly current bedded, with flint pebbles smaller and sparser than in many other localities. The whole section is crowded with fossils, either whole and very friable, or forming seams of comminuted shells. Only a few species are common, with scattered rarities, and there is a marked contrast with the far more marine fauna which was found in the railway tunnel, perhaps at a slightly lower horizon. This occurrence of the marine, Oldhaven type (tunnel) and the" estuarine" Blackheath type (Rock-pit) in such a limited area, caused Whitaker and Stamp to use both terms in their descriptions of the place. At the top of the section, following the slope of the ground rather than forming a definite horizon, the beds are indurated into a conglomerate of flint pebbles, oyster and " Cyrena" shells, which is the" rock" for which the pit was opened. Unconsolidated beds are seen to pass laterally into the conglomerate. By discussion on the spot we saw that we had before us a
220
A. WRIGLEY,
striking case of the problem of derivative fossils. The large Ostrea bellovacina found here are often bivalve and frequently seen grown to flint pebbles. They could not have travelled far and must have lived in the sea upon a pebbly bottom. This observation on the Rock-pit was clearly made in 1813 by Townsend in his Character oj Moses, and he adds: "There are many single shells which are worm-eaten or covered by Serpulae." These are the " Cyrena" which are so common and which abound in the Woolwich shell-beds below, where they are bivalve. Remembering that the Blackheath beds mark a marine transgression over a lagunar continental margin, it seems highly probable that masses of Woolwich-bed shells were swept into the Blackheath Sea and re-deposited there in these current-bedded sands. Probable derivatives of this kind are marked * in the following list. The previously published faunal lists for " Sundridge Park" combine the Rock-pit and the tunnel' into one locality, so it seems desirable to record what we found in the Rock-pit alone, during our visit or in preparation for it. Fossils of the Blackheath Beds in the Rock-Pit at Elmstead Woods. A-abundant, C-common, R-rare. Obsolete generic names are within square brackets. C. Serpula sp. grown upon" Cyrena." R. Discinisca Jerroviae Muir-Wood, a brachiopod found inside bivalve Ostrea: although it occurs rarely in the Woolwich Beds, its present situation and its great fragility preclude the idea of derivation. R. Nucula fragilis Desh. *R. [Area] Barbatia modioliformis (Desh.), [Pectunculus] Glycymeris plumsteadiensis (J. Sby.). A. Ostrea bellovacina Lam. *R. O. tenera J. Sby., always broken, never bivalve. *A. [Cyrena] Corbicula cuneiformis (J. Sby.), *C. C. cordata (Mor.), usually broken. R. Phacoides 2 spp., minute and bivalve. C. [Corbulomya] Lentidium antiquum (Desh.), bivalve. C. [Corbula] Aloidis arnouldi (Nyst). R. A. morrisi Edw. MS. [=regulbiensis var, B Morris]. R. Theodoxus subornatus (d'Orb.) with colour markings. R. Theodoxus uniplicatus (J. de C. Sby.), * " Hydrobia " parkinsoni Morris R. Melanopsis sp., broken. *C. "Melania" inquinata Defr. *c. Tympanotonus funatus (Mant.). R. Calyptraea sp. . R. Murex abbatiae Wrig. R. Pollia lata (J. Sby.]. *C. "Planorbis" hemistoma J. Sby. 1 Meyer's collection of fossils from the Elmstead Woods railway tunnel is preserved in the Sedgwick Museum, Cambridge, together with his MS. list of them.
PROC. GEOL.
Assoc.,
VOL.
LVI (1945.)
PLATE
9
[Photo: G. Austin Browne.
A.-BLACKHEATH BEDS, WITH SHELLS AND ELMSTEAD WOODS.
PEBBLES;
ROCK-PIT,
[Photo: A. J. Bull. B.-FOSSILIFEROUS BLACKHEATH BEDS; ROCK-PIT, ELMSTEAD WOODS.
[To face p, 220.
FIELD MEETING AT ELMSTEAD WOODS, KENT.
221
The decayed condition of the majority of these mollusca, whose shells are of aragonite, is strongly contrasted with the unaltered calcite of the Ostrea. One sometimes wonders if the unfossiliferous condition of many exposures of Blackheath beds is due to their decalcification, but were this so the oysters, which always are present among the fossils, would surely have remained. Mr. H. W. Harrison kindly permitted us to visit the Rock-pit, Dr. Himus was Field Meeting Secretary, and we are indebted to Dr. A. J. Bull and to Mr. G. Austin Browne for the photographs of this noteworthy section, reproduced on plate 9, which give a general impression of the current bedding and the projecting masses of " rock" in the upper part and adds the detail of a 4-inch band of flint pebbles and fossil shells.
REFERENCES 1811. Organic Remains of a former World, vol. iii, p. 213. TOWNSEND, 1813. The Character of Moses established for Veracity as an historian, pp, 251, 257. BUCKLAND, W. 1817. Trans. Geol. Soc., vol. iv, pp. 277MANTELL, G. A. 1844. Medals of Creation, vol, i, p. 385. WHITAKER, W. 1889. Geology of London, vol. i, p. 227. STAMP, L. D. 1920. Proc. Geol. Assoc., vol. xxxi, pp. 151-3, with further references'. PARKINSON,
J. J.