196 GEOLOGY. 



found, was vertebrated like the old Jurassic birds, but probably 

 shorter and less reptilian. In size they were not larger than pigeons,, 

 but were capable of flight. 



Three others resembled the last in the possession of teeth, which, 

 however, were placed in grooves in place of sockets. They had 

 no keel, but on the other hand had ordinary bird vertebrae. Two 

 of these, namely, Hesperornis regalis and Lestornis crassipes, were of 

 gigantic size, the former being five and a half feet high, and the 

 latter six feet. This combination of fish, reptile and bird characters 

 is so unique that Marsh has erected out of them two new orders 

 OdontotormiE (socket-toothed), and Odontolcce (teeth in grooves), and 

 a new subclass Oddntornithes. (toothed birds). It is remarkable 

 that the presence of these toothed birds in the Niobrara group era 

 birds that had not yet been entirely separated from the fish and 

 reptile classes is exactly what the doctrine of evolution demands. 

 Modern birds are the most specialized of all animals, but these old 

 Cretaceous forms raise the dbubt whether they are most reptile or 

 most bird. They are a transition form between the two classes. 



From these brief outlines, it is evident that there was a most vig- 

 orous life during the Niobrara group times. The oceans swarmed 

 with many kinds of fishes, a large proportion of which were ra- 

 pacious. Gigantic reptiles flourished on sea and land. Flying- 

 saurians navigated the air; many of them of huge size. Reptilian 

 birds abounded, of all sizes, from diminutive forms to gigantic di- 

 mensions. During the earlier and middle portion of this era, the 

 Niobrara ocean was connected on the west with the Pacific. Later r 

 the sea bottoms were raised up along the Rocky Mountain chain, 

 giving access and egress alone from the Gulf on the south, and the 

 Arctic Ocean on the northwest. A slow process of elevation con- 

 tinued on the east as well as on the west, contracting this ocean to 

 ever narrower limits. A reverse movement was now going on 

 from what was taking place early in its history. Then it was in 

 process of subsidence, now it was in process of slow elevation. 

 When sand bars eventually were thrown across the channels of 

 moving waters, much of its life was imprisoned and gradually de- 

 stroyed. The most vigorous species and individuals would last the 

 longest, but all eventually had to submit to the inexorable fate of 

 final extinction. 



