324 HISTORICAL PALAZON TOLOGY. 
the White and Red Crags,—and one belongs to the Newer 
Pliocene, viz., the Norwich Crag. 
The White or Coralline Crag of Suffolk is the oldest of the 
Pliocene deposits of Britain, and is an exceedingly local for- 
mation, occurring in but a single small area, and having a 
maximum thickness of not more than 50 feet. It consists of 
soft sands, with occasional intercalations of flaggy limestone. 
Though of small extent and thickness, the Coralline Crag is of 
importance from the number of fossils which it contains. The 
name ‘ Coralline” is a misnomer; since there are few true 
Corals, and the so-called “ Corals” of the formation are really 
Folyzoa, often of very singular forms. ‘The shells of the Coral- 
line Crag are mostly such as inhabit the seas of temperate 
regions; but there occur some forms usually looked upon as 
indicating a warm climate. 
The Upper or Red Crag of Suffolk—like the Coralline Crag 
—has a limited geographical extent and a small thickness, 
rarely exceeding 40 feet. It consists of quartzose sands, usu- 
ally deep red or brown in colour, and charged with numerous 
fossils. 
Altogether more than 200 species of shells are known from 
the Red Crag, of which 60 per cent are referable to existing 
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 A/ol/usca, the Red Crag contains the ear-bones 
of Whales, the teeth of Sharks and Rays, and remains of the 
Mastodon, Rhinoceros, and Tapir. 
The (ewer Pliocene deposits are represented in Britain by 
the Worwich 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 as a local sea-deposit near the mouth of an ancient 
river. It contains altogether more than roo marine shells, 
of which 89 per cent belong to existing species. Of the 
Mammals, the two most important are an Elephant (/ephas 
werwionalis), and the characteristic Phocene Mastodon (J/. 
