JURASSIC PERIOD. 451 



(although begun long before, as regards some of its subordinate ridges)^ 

 we may infer that the condition mentioned as characteristic of the Tri- 

 assic period — a shallow submergence beneath an inland sea (p. 423) 

 — was followed in the Jurassic period by a somewhat deeper submer- 

 gence, or at least that the waters communicated directly with the 

 ocean, so that marine life once more covered the Rocky Mountain 

 region, from Kansas westward beyond the summit of the chain, even 

 to the Pacific, and that, in these shallow seas, limestones were forming 

 again, as in the later half of the Carboniferous age. 



The absence of sea-shore Jurassic beds from the Atlantic border 

 leads to the same conclusions with regard to the coast, in the Jurassic 

 period, that were deduced for the Triassic (p. 422). 



The Jurassic period commenced in England with the marine de- 

 posits of the Lias. Through the era of the Oolite, the alternations 

 were very numerous, indicating oscillations between clear seas and 

 shallow water or half-emerging land, in the course of which there were 

 coral reefs in England and Europe. The evidences of shallow water 

 and emerging flats increase toward the close of the period, dry-land 

 intervals begin to predominate over the marine, and finally the rock- 

 formations are partly those of lakes and estuaries. The history in 

 Europe in part runs parallel with this, although with many local pecu- 

 liarities. 



The position of the Jurassic beds across England, on the east of the 

 older parts of the island, and their continuation over parts of northern 

 France, correspond with the view that they were formed on the bor- 

 ders of a German Ocean basin. This is well shown, as regards Eng- 

 land, on the map on p. 344. 



While, in both Europe and America, the Triassic period was, in the 

 main, one of great marine marshes and shallow waters, the Jurassic 

 was in both as generally characterized by moderately deep waters and 

 open continental seas. 



Life. — It is evident from the review that Conifers, Tree Ferns, and 

 Cyeads gave character to the forests of the Jurassic world ; while Rep- 

 tiles and Marsupials were the dominant types of the fauna. Reptiles 

 were preeminent in each of the three elements, — in place of whales 

 in the water, of beasts of prey and herbivores on the land, and of 

 birds in the air. 



The multitudes of Reptilian and other remains, entombed in the 

 Stonesfield slate, the Wealden, and the beds at Solenhofen, do not indi- 

 cate an excess of population about these spots. They point out only 

 the places where the conditions were favorable for the preservation of 

 such relics ; they in fact prove that the land was everywhere covered 

 with foliage, and swarming with life. 



