3 36 HISTORICAL PALZONTOLOGY. 
this age under the heads of (1) 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-GuaciaL Deposirs.—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 (Cavs /upus), Red 
Deer (Cervus elaphus), Roebuck (Cervus capreolus), Mole 
(Talpa Europea), and Beaver (Castor fiber), living in western 
England side by side with the “/7ppopotamus major, Elephas 
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 (Z7ogon- 
therium Cuvieri), of the Caledonian Bull or “ Urus” (Bos 
primigenius), and of a Horse (Zguus 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- 
