612 STRATIGRAPHICAL GEOLOGY 



theoretical views, and must be received with great caution ; for 

 it is obvious that, owing to the special conditions under which 

 Glacial deposits have been accumulated, ordinary stratigraphical 

 principles cannot be applied to them. 



Neither are the organic remains which occur in the Gkcial 

 deposits to be trusted as implicitly as those of other series of strata, 

 because portions of an older deposit have sometimes been trans- 

 ported and mixed with newer accumulations. Bones of Mammalia 

 are occasionally found in the Glacial Series and more frequently 

 in Non-Glacial deposits, and they do afford a certain criterion of 

 age, as some of them belong to extinct species and they occur in 

 different assemblages which seem to have succeeded one another. In 

 this way three divisions of Pleistocene time have been distinguished, 

 (1) a time when Elephas antiquus, Rhinoceros Mercki ( = R. lepto- 

 rhinus), and Machcerodus were common animals ; (2) a time when 

 Elephas primigenius (the Mammoth), Rhinoceros tichorhinus, and 

 Hyceana spelcea took their places ; and (3) a period when the Eein- 

 deer (Cervus tarandus) ranged over the greater part of Europe, 

 accompanied by many other existing species of animals which live 

 now within the Arctic Circle. 



Lastly, it was during the Pleistocene period that man appeared 

 in Europe, and one of the special characteristics of man is that he is 

 a manufacturer of implements. Accordingly implements fashioned 

 by the hands of men are found here and there even in early 

 Pleistocene deposits ; the older tools being always made of stone and 

 roughly manufactured, but those of the later phases of the period 

 showing more and more careful shaping and finishing. Stone 

 implements thus afford another means of correlating the Non- 

 Glacial deposits of different districts and countries, but they are 

 rarely found in or under the Glacial deposits. 



The division into Glacial and Non- Glacial is therefore the 

 only arrangement under which the Pleistocene deposits can be 

 conveniently described, and this will be adopted in the following 

 pages ; but the reader must remember that the two sets of deposits 

 are more or le^s contemporaneous. 



With respect to the life of the period, it will be convenient to 

 defer giving a list of the Pleistocene Mammalia till we deal with 

 the Non-Glacial deposits in which they are most frequently found, 

 but mention may be made of the marine shells which often occur 

 in Glacial deposits and in beds associated with them. Those which 

 actually occur in boulder - clays are generally broken, but those 

 found in the interstratified sands and gravels are often perfect. 



The marine niollusca of Pleistocene times all belong to living 

 species, but those found in the Glacial deposits are such as live 



