33 6 HISTORICAL PALEONTOLOGY. 



species. The shells indicate, upon the whole, a temperate or 

 even cold climate, decidedly less warm than that indicated by 

 the organic remains of the Coralline Crag. It appears, there- 

 fore, that a gradual refrigeration was going on during the 

 Pliocene period, commencing in the Coralline Crag, becoming 

 intensified in the Red Crag, being still more severe in the 

 Norwich Crag, and finally culminating in the Arctic cold of the 

 Glacial period. 



Besides the Mollusca, the Red Crag contains the ear-bones 

 of Whales, the teeth of Sharks and Rays, and remains of the 

 Mastodon, Rhinoceros, and Tapir. 



The Newer Pliocene deposits are represented in Britain by 

 the Norwich Crag, a local formation occurring near Norwich. 

 It consists of incoherent sands, loams, and gravels, resting in 

 detached patches, from 2 to 20 feet in thickness, upon an 

 eroded surface of Chalk. The Norwich Crag contains a mix- 

 ture of marine, land, and fresh-water shells, with remains of 

 fishes and bones of mammals ; so that it must have been de- 

 posited at a local sea-deposit near the mouth of an ancient 

 river. It contains altogether more than 100 marine shells, 

 of which 89 per cent belong to existing species. Of the 

 Mammals, the two most important are an Elephant (Elephas 

 meridionalis} , and the characteristic Pliocene Mastodon (M. 

 Arvernensis} , which is hitherto the only Mastodon found in 

 Britain. 



According to the most recent views of high authorities, 

 certain deposits such as the so-called " Bridlington Crag " - of 

 Yorkshire, and the " Chillesford beds " of Suffolk are to be 

 also included in the Newer Pliocene, upon the ground that 

 they contain a small proportion of extinct shells. Our knowl- 

 edge, however, of the existing Molluscan fauna, is still so far 

 incomplete, that it may reasonably be doubted if these sup- 

 posed extinct forms have actually made their final disappear- 

 ance, whilst the strata in question have a strong natural con- 

 nection with the " Glacial deposits," as shown by the number 

 of Arctic Mollusca which they contain. Here, therefore, these 

 beds will be included in the Post-Pliocene series, in spite of 

 the fact that some of their species of shells are not known to 

 exist at the present day. 



The following are the more important Pliocene deposits 

 which have been hitherto recognized out of Britain : 



I. In the neighborhood of Antwerp occur certain "crags," 



