1867.] DAWKIN-S SLOWER BEICK-EAETHS. 91 



On the Age of the Loweb Beick-earths of the Thames Valley. 

 By W. Boyd Dawkii^s, Esq., M.A. (Oxon.), E.G.S. 







Contents. 





1. 



Introduction. 





5. 



Testacea. 



2. 



Literature. 





6. 



Mammalia. 



3. 



Sections. 

 a. Ilford. 



/3. Grays Thurrock. 

 y. Crayford. 

 d. Erith. 







a. List of species. 

 (3. Eange of species, 

 y. Eelation to Praeglacial 

 and Postglacial Fauna. 







7. 



The Lower Brick-earth not 





6. Wickham. 







late Postpliocene. 



4. 



Inferences from Sections 



. 



8. 



Summary. 



■§ 1. Introduction. — While engaged in accunmlating materials for 

 the definition of the range in space and time of the British Pleisto- 

 cene Mammalia, I was forcibly struck by the peculiar character of 

 those found in the Brick- earths and gravels of the lower part of the 

 Thames Yalley, as compared with those from low-level deposits in 

 other parts of Britain which seem stratigraphically to be of the same 

 date, and which occupy the same horizon above the sea. I propose, 

 therefore, to bring before the Society an analysis of my notes re- 

 lating to the remains found on the north side of the Thames, at 

 Ilford and Grays Thurrock in Essex, and on the south side at 

 Crayford, Erith, and Wickham in Kent, together with some notices 

 of the strata in which they occur. 



§ 2. Literature. — The first to call attention to these deposits was 

 Professor Morris, who published a valuable paper on Grays Thur- 

 rock, in 1836*, and extended his investigations in 1838t to the other 

 localities under consideration. After a careful analysis of the evi- 

 dence aftbrded by the mollusca, he inferred that " their connexion 

 with the ancient beds of gravel was a subject requiring further 

 elucidation," and abstained from drawing any conclusions about 

 their exact age. Dr. Ealconer, in 1857$? in his masterly treatise on 

 the Mastodon and Elephant, recognized " the true Pliocene assem- 

 blage of species " at Grays Thurrock and the lower beds at Brent- 

 ford, and thence inferred that they were of an earlier age than any 

 part of the Till or Boulder- clay. Mr. Prestwich, on the other hand, 

 in 1864, considered the deposits at Ilford to belong to the Qua- 

 ternary Low-level Gravels of the Thames Yalley, and to be of " late 

 Postpliocene age"§, while Mr. Searles Wood, jun., expressed in 

 1866 II his conviction that the series at Ilford, Erith, and Wickham, 

 which he terms the Lower Brick-earth, is " in age younger " than 

 the Boulder-clay, and older than, as well as distinct from, those at 

 Grays Thurrock. The discussion of these conflicting views we must 

 defer until we can collect evidence both physical and palaeontolo- 

 gical on the subject. 



* Mag. of Nat. Hist. (Loudon's), 1836. 



t Ann. & Mag. of Nat. Hist. 1838. 



J Quart. Journ. Geol. Soc. vol. xiv. p. 83, 1858. 



§ G-eological Magazine, vol. i. p. 245, 1864. 



II Geological Magazine, vol. iii. pp. 59-61, 1866. 



