GEOLOGICAL SURVEY OF FORTIETH PARALLEL. 311 



strata which occupy much of Colorado, Utah, and Nevada, scarcely 

 reach eastward beyond the mountains ; and the Cretaceous age was 

 marked by a great submergence which carried the shore - line pro- 

 gressively from the Gulf of Mexico to the Wahsatch, and northward, 

 perhaps, to the Arctic Sea, converting all the area between the Wah- 

 satch Mountains and the Canadian highlands into a sea, in which were 

 deposited in some places 2,000 feet of limestone, the slow accumula- 

 tion of calcareous matter from the growth and decay of marine organ- 

 isms. 



From Mr. King's careful study of the Mesozoic rocks of Nevada, 

 we learn that the Trias consists of alternations of limestone and quart - 

 zite, which, in Star Peak, form a continuous section of over 10,000 

 feet. The fossils which the limestones contain show that much the 

 larger part of this mass belongs to the Alpen Trias of the Old World, 

 the Halstadt and Saint Cassian beds, and those which form the pas- 

 sage to the Jura. 



The Jurassic rocks of Nevada are mostly shales the deposits from 

 water too shallow for limestones and contain few fossils. Along the 

 eastern margin of the Jurassic area in the Black Hills, the Jurassic 

 beds are more purely marine, and are far richer in fossils. The upper 

 portion of these beds, which are of an estuarine or littoral character, 

 has lately been discovered to be a vast cemetery of vertebrate animals, 

 some of which are of unequaled size, and in their structure of special 

 interest. Among these are the huge dinosaurs described by Marsh and 

 Cope, some of which far exceed in dimensions any terrestrial animals 

 before known, the largest, according to Marsh, having a length of at 

 least one hundred feet, and a height of twenty-five or thirty. 



The uppermost member of Mr. King's Mesozoic section is the some- 

 what famous Laramie groxip the Lignitic formation of Dana, so 

 named because it contains the most important coal-beds of Colorado. 

 The age of this group of rocks has been much discussed by Dr. Hay- 

 den and Lesquereux, the distinguished fossil botanist, and it has been 

 represented by them to be Tertiary, on the evidence of its numerous 

 fossil plants ; Cope, however, found the remains of Cretaceous verte- 

 brates, and Meek, Cretaceous mollusks, in it ; and hence it was said to 

 have a Cretaceous fauna and a Tertiary flora. The writer has, how- 

 ever, for a long time contended that its flora was distinct from that of 

 the Tertiary rocks, and the proof was stronger that it was Cretaceous. 

 Mr. King adduces new and apparently conclusive evidence that it is 

 older than the Tertiary, since, like Cope, Meek, and Stevenson, he has 

 obtained numerous Cretaceous animal remains from it, and finds it to 

 underlie unconformably the Coryphodon beds, the oldest portion of the 

 Eocene. 



Tertiary. The pictures which geology presents to us of the far 

 West during the Tertiary age are totally different from those which 

 preceded them, and, on the whole, more varied and interesting. As 



