THE .IUI?A. 151 



Carboniferous and the Red Beds, and on the other between the Red Beds 

 and the Jura. In the Black Hills, however, no such unconformity is to be 

 found. 



SECTION VII. 

 THE JURA. 



The Jurassic system, which is so largely developed in Europe, con- 

 taining- the remains of huge swimming and flying reptiles and holding im- 

 mense deposits of iron ore that are the foundation of some of the largest 

 iron industries in England and the Continent, is but sparingly represented 

 in American geology, and none of the gigantic vertebrates have as yet been 

 found here. For a long time the Trias of the Atlantic coast, especially in 

 the coal basins of Richmond and North Carolina, was regarded by some of 

 our most eminent geologists as in whole or part of Jurassic age, but that 

 view is now abandoned,.and the only developments of undoubted Jurassic 

 rocks in our country lie west of the Mississippi. 



The first determination of the formation in the Far West was made by 

 Professor Meek from fossils collected in the Black Hills by Dr. Hayden in 

 1857, and the discovery was announced by Meek and Hayden in a paper 

 published in the Proceedings of the Acadeuiy of Natural Science of 

 Philadelphia in March, 1858. 



The forms there made known are all molluscan, excepting one crinoid, 

 Pentacrinus asteriscus, and are closely allied to species of the European 

 Jura. 



Since that announcement it has been found that the formation is very 

 generally present in the Rocky Mountain system from the extreme north 

 to New Mexico and from their eastern slope westward in the various ranges 

 to the Wasatch. It is known, too, in the great interior basin and in the 

 Sierra Nevada. For the most part, it has been identified by its fossil con- 

 tents, but there are considerable districts Avhere these guides are wanting 

 and it has been traced merely by stratigraphical relations and lithological 

 resemblances. In the mountain chains of the Northwest, the Laramie 

 Mountains, the Wind River Mountains, the Bighorn Mountains, etc., it is 

 often richly fossiliferous, but less so than in the Black Hills. In the Hills 



