264 



SCIENCE-GOSSIP. 



PLEISTOCENE BEDS OF LOWER THAMES VALLEY. 



By A. Saxter Kexxard. 



T T is indeed a pleasure to welcome any new 

 worker in the field of geology, a branch of 

 science which apparently, though perhaps tem- 

 porarily is lacking in enthusiastic supporters. 

 Hence the perusal of Mr. J. P. Johnson's paper 

 on "Pleistocene Drift of Thames Valley" in the 

 December number of Sciexce-Gossip afforded me 

 great satisfaction. In welcoming him as a worker 

 in the more recent deposits, he may be assured that 

 the field is large and the workers but few, whilst 

 the literature, no small item, will well repay a 

 careful perusal. Unfortunately a large amount of 

 the published work is so scattered that it entails 

 much labour to examine, and it is to this cause 

 that the errors which have crept into Mr. Johnson's 

 paper are to be ascribed. 



Speaking broadly, the deposits may be divided 

 into three sections, the high-level gravels, the low- 

 level gravels and the brickearths. In the first 

 large numbers of flint implements have been 

 found, many of which show little or no traces 

 of abrasion. Mammalian remains are scarce, 

 though not unknown, as stated by Mr. A. E. 

 Salter, F.G.S. ( J ) The human remains from 

 Galley Hill, Swancombe, belong to this series. 

 In the low-level gravels flint implements are 

 scarce, and are nearly always abraded. Bones 

 are also extremely rare. 



There can be no doubt that the constituents of 

 the low-level gravels have been largely derived' 

 from the high-level gravels. The most recent 

 deposit, the brickearths, are of interest from the 

 standpoint of the palaeontologist, as it is in these 

 deposits that themolluscan and vertebrate remains 

 are most abundant. It is at once evident that the 

 physical conditions under. which these deposits 

 were laid down differ widely, and the amount of 

 time required to account for the various changes is 

 indeed enormous. 



Mr. Johnson is undoubtedly right in assuming 

 that the Thames was considerably larger when 

 these deposits were laid down than it is now. We 

 know that the drainage area of the Thames has 

 been in the past, and is still being, decreased through 

 other streams tapping its sources and its tributaries. 

 The Severn now takes into the Bristol Channel a 

 large amount of drainage which at one time went 

 into the Thames. The Medway also has diverted 

 waters which previously flowed into the Darenth. 

 The Lea and the Kennett have likewise had their 

 drainage basins considerably reduced. I do not 

 think, however, that there are any grounds for its 



f 1 ) A. E. Salter : " Pebbly and other Gravels in Southern 

 tngland. Proc. Geol. Assoc, vol. sv. p. 274. 



supposed more torrential character, for even if 

 this were so with regard to the gravels, the brick- 

 earths point to a placid stream. In any case 

 our knowledge of river action must be greatly 

 enlarged before we can reason from the known 

 to the unknown. 



As to the suggestion that the land stood higher, 

 I do not think that the facts bear this out. In 

 describing the Pleistocene Mollusca of Crayford (-) 

 mention was made that I had obtained an example 

 of Littorina rudis Maton from the brickearth, and 

 it was pointed out that the example was a dwarfed 

 form, and resembled those now living at Tilbury. 

 I also stated that " the presence of this species, 

 together with Paludestrina ventrosa, already known 

 from these beds, undoubtedly points to the prox- 

 imity of estuarine conditions." Since then I 

 have obtained numerous examples of L. rudis. At 

 the present day this form only struggles up the 

 river as far as Tilbury, hence we must conclude 

 that marine conditions were more pronounced than 

 they are at present. Mr. Johnson's statement 

 that these beds are locally post-glacial is mis- 

 leading. That these deposits are newer than the 

 boulder clay is admitted on all hands. Still, 

 although the last word on the Thames Valley 

 deposits has not yet been said, there is strong 

 evidence in favour of the view that the low-level 

 gravels were accumulated during a period of intense 

 cold, whilst the brickearths are overlain by the 

 "Warp" and "Trail," and are, therefore, inter- 

 glacial. Mr. Johnson is in error in stating that 

 only three species of the Mollusca are extinct in. 

 this country, as besides Unio littoraiis, Corlicuia 

 fluminalis and Paludestrina marginata mentioned by 

 him, Eulota (Helix) fruticum is known from Ilford,. 

 and Dr. J. Gwyn Jeffreys has recorded Pyramidnla 

 (Helix) ruderata from the same locality. A variety 

 of Sphaerium comeum from Crayford, figured in 

 Sciexce-Gossip (N.S. vol. ii. p. 39) is also quite 

 unknown in a living state in this country. On the 

 Continent it is considered a good species and 

 named Sphaerium maenanum Kobelt. It is a rare form, 

 living in the River Main. I have also examined 

 other varieties of several species which cannot 

 be matched by recent British forms. Amongst 

 them an example of Limnaea palustris, from Ilford, is- 

 noteworthy. It was found by my friend, Dr. Frank 

 Corner, a geologist whose knowledge of the alluvium 

 and pleistocene deposits of the Thames Valley is 

 unequalled, and to whom I am indebted for much 

 information. On submitting it to Dr. O. Boettger, 

 of Frankfort, he pronounced it as quite new to 



( s ) Science-Gossip, N.S. vol. ii. pp. 39, 40. 



