348 



SCIENCE-GOSSIP. 



GEOLOGY 





CONDUCTED BY EDWAEB A. MARTIN, F.G.S. 



Drift Nomenclature. — Every one must cor- 

 dially endorse Mr. Mai'tin's remarks (ante p. 318) 

 as to the desirability of adhering to one system 

 of nomenclature with regard to drift deposits, yet 

 the difficulty of framing such a system is only too 

 obvious. As our knowledge is extended so will 

 our nomenclature be altered, and the introduction 

 of new terms or the different application of well- 

 established names must, for a time at least, cause 

 a little confusion. Another source of error is 

 personal opinion, and arises from different views 

 as to the correlation of the various deposits. It 

 is to both these causes that the differences between 

 Mr. Salter's views and mine are to be ascribed. 

 Every geologist must admire the amount of good 

 work which Mr. Salter has accomplished in the 

 gravels of the South of England, and it is with 

 great relvictance that I differ from him. As I 

 understand Mr. Saltei', he charges me with using 

 inappropriate terms and with misquoting him. 

 Hence a criticism of his paper is the best means of 

 refuting these statements. Mr. Salter's views were 

 given in " Pebbly and other Gravels in Southern 

 England" (Proc. Geol. Assoc, vol. xv., pp. 264- 

 286). He has divided what he calls " The Thames 

 Valley Gravels " into three series, as stated by 

 Mr. Martin: (1) The high level or early drifts; 

 (2) Lower plateau and glacial drifts; (3) The 

 river drifts. I intend dealing here only with those 

 which belong to the lower Thames. In the first 

 group he places Swanscombe Hill, Ash, Well Hill, 

 Shooter's Hill, and West Ho HiU. The well- 

 known deposits at Ash and on the chalk plateau 

 were called by the late Sir Joseph Prestwich 

 " The chalk plateau drifts," and this name, I 

 think, should be retained. To correlate the other 

 deposits with those at Ash is, in my opinion, 

 founded on very slight evidence, and to connect 

 them with the Thames is "avast retui-n of theory 

 for a very small investment of facts." Mr. Salter 

 is now inclined to call them Pliocene. They may 

 be, but the onus prohandi is on his shoulders. 

 Well Hill deposit is a mere patch, and West Ho 

 Hill is no better. There is no section at Swans- 

 combe Hill, and the Shooter's Hill deposit is 

 claimed by Mr. Goodchild as of " glacial origin.'" 

 Hence I would submit that it is better to speak of 

 these gravels as of " doubtful age, perhaps con- 

 nected with the initial stages of the Thames." 

 In his second series, " the lower plateau and 

 glacial," Mr. Salter places Limpsfield Common, 

 Farley Hill, Boughton Hill, and Dartford Heath. 

 He also states (p. 274) : " No contemporaneous 

 fossils, such as large mammalia, have been re- 

 corded from this set of gi-avels." In the first 

 place, the application of the term " lower plateau 

 or glacial" to these gravels is quite new. Sir 

 Joseph Prestwich speaks of this stage as the 

 " High level or Limpsfield gravel stage." It is to 

 this series that I applied the term " high level," 



so if I have erred, I am in good company. 

 Mr. F. C. J. Spurrell has stated that the oldest 

 deposit of the Thames " is the widely-spread tract 

 of Dartford gravel (the highest terrace), extending 

 many miles on either side of the present river. 

 This gravel contains palaeolithic implements." 

 Sir Joseph Prestwich notes " The gravel at Dart- 

 ford forms part of the great sheet which extends 

 westward over Wilmington and Dartford heaths, 

 and eastward to Stone and Milton Street, near 

 Swanscombe." Mr. Salter, however, considers 

 the gravel of Galley Hill as not belonging to this 

 but to his third series, and is thus opposed to 

 both Sir Joseph Prestwich and Mr. Spurrell. 

 Personally I feel confident that Mr. Salter is in 

 error, and if only he would re-examine the grou.nd 

 he would doubtless recant his views. The human 

 remains from Galley Hill are not the only known 

 contemporary fossils from the Dartford gravels : 

 Dr. Corner has a tusk of hippopotamus from 

 Milton Street; Mr. Elliott has a deer's antler and 

 foot bones of Felis leo from near Swanscombe, at 

 the same level ; Mr. Spurrell has found Elephas 

 primigenius, Rhinoceros, Bos, Equus, and Cervus, in 

 the small patch of gravel near Northfleet Station, 

 and the same species in the similar terrace gravel 

 at Dartford Brent, west of the city asylum, 

 besides other remains at intermediate localities. 

 Hence it will be seen that contemporary fossils 

 do occur in Mr. Salter's second series, and he 

 must either withdraw his negative, or else, in 

 opposition to all authorities, withdraw the Dartford 

 Gravel from his second series. I would strongly 

 object to Mr. Salter's terms, "lower plateau and 

 glacial." The term "plateau drift" has been 

 applied to the Ash beds, and to prevent confusion 

 it had better be confined to them. As to the use 

 of the adjective glacial, if it implies the origin, 

 it is incorrect; if it implies age, it is mis- 

 leading. It is far better to restrict the term 

 " glacial " to the method of deposition, and hence 

 I still maintain that it is better to use the term 

 of Sir Joseph Prestwich — "high level." In his. 

 third series — "the river drifts" — Mr. Salter has 

 included deposits of various ages and manner of 

 deposition. As I have already shown, the Galley 

 Hill deposit, which he places here, rightly belongs 

 to his second series. The gravel near Hayes 

 Station, in the valley of the Eavensbourne, and 

 the Green Street Green deposit in that of the 

 Cray are not river drifts at all. As was pointed 

 out years ago by Charles Darwin, they denote a 

 much colder climate when the district was biu'ied 

 dviring winter in snow, and the ground frozen. 

 In summer time the snow would melt rapidly, and 

 would sweep the ddbris lying on the higher ground 

 into the valleys. No one who has seen a true river 

 gravel would consider this mass of unstratified 

 and little-worn mass of flints as of river origin. 

 If Mr. Salter would correctly apply the term 

 " glacial," it should be to this deposit rather than 

 the Dartford gravel. To lump this deposit with 

 the Palaeolithic gravels and the Crayford brick- 

 earths, is a course which commends itself to few 

 of the students of Pleistocene geology. I started 

 these remarks with the intention of proving cer- 

 tain statements that I had previously made. 

 Whether I have done so, I leave your readers to 

 judge. I would justify it by the fact that it is 

 only by free discussion of differences such as these, 

 that we can arrive at the truth. — A. Santer 

 Kennard, Beneden, Mackenzie Road, Beckenham. 



