336 HISTORICAL PALEONTOLOGY. 



this age under the heads of (i) Pre-Glacial deposits, (2) Glacial 

 deposits, and (3) Post-Glacial deposits, according as they were 

 formed before, during, or after the " Glacial period." It can- 

 not by any means be asserted that we can definitely fix the 

 precise relations in time of all the Post-Pliocene deposits to the 

 Glacial period. On the contrary, there are some which hold a 

 very disputed position as regards this point; and there are 

 others which do not admit of definite allocation in this manner 

 at all, in consequence of their occurrence in regions where no 

 " Glacial Period " is known to have been established. For 

 our present purpose, however, dealing as we shall have to do 

 principally with the northern hemisphere, the above classifi- 

 cation, with all its defects, has greater advantages than any 

 other that has been yet proposed. 



I. PRE-GLACIAL DEPOSITS. The chief pre glacial deposit of 

 Britain is found on the Norfolk coast, reposing upon the Newer 

 Pliocene (Norwich Crag), and consists of an ancient land-sur- 

 face which is known as the " Cromer Forest-bed." 



This consists of an ancient soil, having embedded in it the 

 stumps of many trees, still in an erect position, with remains 

 of living plants, and the bones of recent and extinct quadru- 

 peds. It is overlaid by fresh-water and marine beds, all the 

 shells of which belong to existing species, and it is finally sur- 

 mounted by true "glacial drift." While all the shells and 

 plants of the Cromer Forest-bed and its associated strata belong 

 to existing species, the Mammals are partly living, partly ex- 

 tinct. Thus we find the existing Wolf (Cants lupus), Red 

 Deer (Cennts claphus), Roebuck (Cennis capreolus), Mole 

 (Talpa Europcea}, and Beaver (Castor fiber), living in western 

 England side by side with the Hippopotamus major, ElcpJias 

 antiquus, Elephas meridionalis, Rhinoceros Etruscus, and R. 

 megarhinus of the Pliocene period, which are not only extinct, 

 but imply an at any rate moderately warm climate. Besides 

 the above, the Forest-bed has yielded the remains of several 

 extinct species of Deer, of the great extinct Beaver (Trogon- 

 therium Cuvierz), of the Caledonian Bull or " Urus " (Bos 

 primigenius\ and of a Horse (Equus fossilis), little if at all 

 distinguishable from the existing form. 



The so called " Bridlington Crag" of Yorkshire, and the 

 " Chillesford Beds " of Suffolk, are probably to be regarded as 

 also belonging to this period; though many of the shells which 

 they contain are of an Arctic character, and would indicate 

 that they were deposited in the commencement of the Glacial 

 period itself. Owing, however, to the fact that a few of the 

 shells of these deposits are not known to occur in a living con- 



