20 LONDON DISTRICT. 



Pectunculus terebratularis Lamarck, a large, thick, sub -orbicular 

 shell, and the small, oval Corbula regulbiensis Morris are among 

 the commonest. Protocardia, Modiola, a species of oyster 

 (probably Ostrea heteroclita Deshayes), and sharks' teeth of the 

 genus Lamna have also been found. The Bottom Bed represents 

 the zone of Cyprina scutellaria. 



In deposits of the Woolwich type there are definite shell-beds 

 consisting of clay crowded with estuarine species. Among these 

 are the trigonal bivalve Cyrena cor data Morris, the longer and 

 more angular C. cuneiformis Ferussac, and the oysters Ostrea 

 bellovacensis Lamarck and 0. tenera J. Sowerby. The univalves 

 include the long-spired Melania inquinata Defrance, orna- 

 mented with blunt spines on the angular keel that runs along 

 the whorls, Potamides (Tympanotonus) funatum (Mantell) and 

 Melanopsis buccinoidea Ferussac. Beds with freshwater shells 

 contain mostly univalves, with occasional examples of the fresh- 

 water mussel Unio. Viviparus lentus (Solander), commonly known 

 as Paludina, a short-spired, round -whorled, unornamented 

 species, is probably the commonest of the univalves. Several 

 species of Neritina, some with wavy colour-stripes still preserved, 

 are recorded, as well as Planorbis, Limncea, and Pitharella, 

 while the tiny shells of Hydrobia occur in profusion. 1 Further 

 interest attaches to the fossils of these beds by the discovery 

 near Croydon of the remains of a large running -bird Gastornis 

 klaasseni E.T. Newton, related probably to the goose-like birds, 

 and bones of Coryphodon croydonensis E. T. Newton, a large, 

 five-toed, herbivorous mammal. The fossils as a whole were 

 considered by Prestwich to be indicative of a climate somewhat 

 warmer than that of the Thanet Sand epoch. 



The total thickness of the series varies from 40 to 90 ft., 

 averaging about 70 ft. Along the southern outcrop there are 

 good sections round Ewell and Sutton ; that at Cheam Brickyard 

 in 1913 was as follows : 



Ft. 



Clayey gravel (Pleistocene) - - 2-5 



Sand and loam, pink, grey, light green, buff, yellow and light mauve - 56 

 Grey-green clay, weathering buff - - 3 



Mottled clay, crimson, magenta, yellow, grey and green - 7 



Sandy loam, green and glauconitic - - \ ^ 



Pebble bed with green-coated flints scattered through loam 3 ft. -j 

 Grey clay with race and nodules - - 3 



Thanet Sand - - seen to 7 



The dip was 6 a little east of north. 



At the famous Nonsuch Pottery sharks' teeth are frequent 

 in the lower beds. Round Croydon many sections have shown 

 the great variability of the formation ; the shell-bed has yielded 

 vertebrate fossils and is underlain by mottled clay of the Reading 

 type. The most famous sections were at Lewisham (Loam Pit 

 Hill) and Charlton 2 but are for the most part built over and 



1 For a list of fossils from the Woolwich freshwater bed, see ' Geology of 

 South London ' (Mem. Geol. Surv.), 1921, p. 22. 



2 See ' Geology of London ' (Mem. Geol. Surv.), vol. i, 1889, pp. 148, 154. 



