202 CASTOKIDJE. 



below the present surface, in places where they may have 

 been overwhelmed by debris, or even buried by man ; and, 

 although these bones are the most recent of all, they are 

 almost always, owing to their superficial situation, the 

 worst preserved." * 



The fossil remains, however, of the Beaver discovered in 

 the lacustrine clay with the submerged forest at Bacton, 

 and those obtained by Mr. Warburton at Southwold, and 

 by Mr. Lyell at Thorpe, from the fluvio-marine crag, carry 

 back the date of this existing species to the pliocene ter- 

 tiary period, when it .was the associate of the Mammoth, 

 Rhinoceros, and Hippopotamus. 



The like antiquity of another and smaller Rodent of the 

 Beaver family, still existing in most of our British rivers 

 and smaller streams and ditches, is more abundantly testi- 

 fied by the numerous fossils of a species of Arvicola, which 

 I have been unable satisfactorily to distinguish from the 

 Arvicola amphibia, or common Water-rat. 



Dr. Buckland appears to have been the first to have 

 noticed the fossil Arvicolee in British localities, observing, 

 with regard to the Kirk dale cavern, that " the teeth which 

 occur, perhaps in greatest abundance, are those of the 

 Water-rat ; for in almost every specimen I have collected 

 or seen of the osseous breccia, there are teeth or broken 

 fragments of the bones of this little animal mixed with, and 

 adhering to, the fragments of all the larger bones. These 

 rats may be supposed to have abounded on the edge of the 

 lake, which I have shown probably existed at that time 

 in this neighbourhood."*!* 



The abundance of these small aquatic Mammals in the 

 Kirkdale cave, at first view suggests a very common con- 



* Cambridge Philosophical Transactions, vol. i. p. 177. 

 t Reliquiae Diluvianse, p. 18. 



