THE QUATERNARY PERIOD. 349 



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 (Canis lupus), Red 

 Deer (Cervus elaphus), Roebuck (Cervus capreolus), Mole 

 (Talpa Euro pact), and Beaver (Castor fiber), living in .western 

 England side by side with the Hippopotamus 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 (Trogon- 

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

 priinigcnius) , 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 known to occur in a living con- 

 dition, these, and some other similar accumulations, are some- 

 times considered as referable to the Pliocene period. 



II. GLACIAL DEPOSITS. Under this head is included a 

 great series of deposits which are widely spread over both 

 Europe and America, and which were formed at a time when 

 the climate of these countries was very much colder than it is 

 at present, and approached more or less closely to what we see 

 at the present day in the Arctic regions. These deposits are 

 known by the general name of the Glacial deposits, or by the 

 more specialized names of the Drift, the Northern Drift, the 

 Boulder-clay, the Till, &c. 



These glacial deposits are found in Britain as far south as 

 the Thames, over the whole of Northern Europe, in all the 

 more elevated portions of Southern and Central Europe, and 

 over the whole of North America, as far south as the 3Qth 

 parallel. They generally occur as sands, clays, and gravels, 

 spread in widely-extended sheets over all the geological forma- 

 tions alike, except the most recent, and are commonly spoken 

 o'f under the general term of " Glacial drift." They vary much 



