246 GEOLOGY. 



tion being retained in others. Now, in all the region 

 where this arrangement is found, there must have been, 

 in the first place, deposits of a marine character, for the 

 Portland stone, A, is filled with marine shells. After- 

 ward these beds were covered with lake or river mud, 

 which became dry land, and was the scene of a forest veg- 

 etation. Then the land sank down, and was submerged, 

 with its load of forest growth, beneath fresh water in 

 place of the salt water which was there before the dirt- 

 bed was laid. From this water the limestone strata, C, 

 were deposited upon the dirt-bed, B, this being demon- 

 strated by the shells in the stone, which are of the kinds 

 that are found only in fresh water. The tilting, which 

 is to the amount of 45 degrees, was not done till all the 

 fresh-water limestones, C, were laid down. 



351. Animals. Animal life had advanced on its forms 

 in the previous age, though the fishes were still only ga- 

 noid and placoid, and the mammalia were still of the mar- 

 supial type. Insects appeared more largely than before, 

 because there was more food for such animals in the veg- 

 etation. " There were," says Page, " burrowers among 

 the decaying timber of the pine forests; leapers among 

 the leaves and herbage of the cycas grove; hunters along 

 the river-bank and across its sunny waters ; and gaudy 

 flutterers over the flowers of the lily and the palm-tree. 

 All the great orders of insect life beetles, cockroaches, 

 dragon-flies, grasshoppers, and ants are abundantly rep- 

 resented." The Crustaceans were numerous, those which 

 were similar to shrimps and lobsters being especially prev- 

 alent. The higher orders of Mollusks abounded. There 

 were still Crinoids, though they were on the wane. Cor- 

 als were abundant wherever the formation of limestone 

 was going on. Sea-urchins also were numerous, one of 

 which is represented in Fig. 146. But the reptilian de- 

 velopment was the great feature of this middle portion of 

 the age of Reptiles. There were reptiles for the ocean, 

 the river and estuary, the muddy shore, and the land ; 



