544 Deposits in the Valley of the Thames 



A List of Shells occurring in the Mammaliferous Deposits. 

 E. Erith. G. Grays. C. Copford. S. Stutton. I. Ilford. 



Having in the preceding observations pointed out the lo- 

 calities, and described the mineral character of the mammal- 

 iferous stratum, it may be interesting to enquire into its com- 

 parative age, and the circumstances under which it was de- 

 posited. The remains, as before stated, belong chiefly to the 

 Ruminanlia and Carnivora, the former of which occur abun- 

 dantly, but the latter are rather sparingly distributed. The 

 bones are seldom much rolled or broken, but are generally 

 well preserved, and frequently perfect ; some indeed appear 

 to have undergone partial decomposition, but this might have 

 been occasioned by exposure to the atmosphere, previously 

 to their becoming imbedded. With these remains are asso- 

 ciated about thirty-eight species of terrestrial and fluviatile 

 Testacea, all of which, with the exception of two species, are 

 still in existence; and the extinction of these two is probably 

 confined to this country, as one of them {Cyrena) appears to 

 be closely allied to a species now living in the Nile, and the 

 other (Unio) strikingly resembles one which inhabits the ri- 

 vers of the south of France.* 



The living genera of some of the Mammalia are now only 

 found in or near the tropical regions ; but as their remains 

 are presumed to have belonged to extinct species, and being 



*See observations by Mr. G. B. Sowerby. 



