204 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DcC. 5. 



anomalous ; on tliis point however Prof. Owen*, speaking of the genus 

 Felis, j^istly observes, '* There is no genus of mammaha in which the 

 unity of organization is more closely maintained, and in which, there- 

 fore, we find so little ground in the structure of a species, though it 

 may most abound at the present day in the tropics, for inferring its 

 special adaptation to a warm climate." 



With regard to the relative age of this deposit, I had formerly 

 considered itf as s}Tichronous mth the numerous mammalian beds 

 which occur throughout the valley of the Thames. The evidence, 

 however, is not very satisfactory, inasmuch as the presence of pebbles 

 apparently derived from the drift might lead to the inference of its 

 being posterior to that period, and the absence of the Paludina mar- 

 ginata, Cyrena trigonula, and TJnio littoralis, may distinguish it from 

 the beds at Ilford, Grays, Erith, &c. 



Still, perhaps, sufficient value has not been assigned to certain 

 specific mammaUan remains of the later tertiary deposits, as tests of 

 their relative position ; nor can we feel the full importance of shght 

 specific difi'erences until we are acquainted with the true and exact 

 value of the succession of the different groups of mammals, during 

 the more recent geological changes ; and the geologist should use 

 great caution in marking the exact bed from whence the remains that 

 he submits to the comparative anatomist are derived, even though he 

 obtain them from the same valley. Independently however of these 

 considerations, there is a singular fact, which must not be overlooked 

 as connected with the present subject, viz. that it is generally along 

 those valleys where the present drainage of the country is effected 

 that we find the most extensive deposits of mammalian remains and 

 recent shells ; and consequently very little alteration can have taken 

 place as regards the physical configuration of the country since the 

 period of their deposition. 



List of Mammalia found at BrentfordX. 



Elephas primigenius. Cemis tarandus. 



Bison priscus. Rhinoceros tichorhinus. 



Bos longifrons. Hippopotamus major. 



Cervus elaphas. Felis spelaea. 



* British Fossil Mammalia, p. 162. 

 t Mag. Nat. History, 1838, p. 539. 



X Mr. Thomas Layton, jun., has presented a collection of the mammalian re- 

 mains to the British Museum. 



