DESCRIPTIONS OF THE FORMATIONS. 43 



That the trap is not confined, however, to the Triassic rock surface, is beauti- 

 fully shown by the very numerous trap-dikes which cut the Highlands of Orange 

 county, N. Y., and of New Jersey ; by the long, straight, narrow dike which issues 

 from the South Mountain, opposite Carlisle, in Pennsylvania, and cuts across all 

 the formations, from the Potsdam up to the Subcarbonif erous, at the mouth of the 

 Juniata, (see notes 9, 77 and 170, in chapter on Pennsylvania), and especially by 

 the still longer trap-dike recently discovered by Prof. Frazer, hi Lancaster county, 

 Pa. , which not only penetrates the Welsh hills of gneiss, but cuts across the west 

 end of the Chester county (Pa.) Valley, near the famous nickel mine, and reaches 

 the Susquehanna River near the roofing slates quarries at Peach Bottom. Lesley. 



The Triassic formation yields the rock-salt and brine of the greater part of 

 Europe, especially in England, Ireland, France, and part of Germany. 



17. Jurassic, The upper portion of what is commonly called the Triassic, on 

 the Atlantic border, may belong to the Jurassic, and is so described by Prof. P. R. 

 Uhler, in the annexed Guide for Maryland ; and by Prof. W. B. Rogers, as Juro- 

 Triassic and Juro-Cretaceous, in Virginia. But there are beds which are 

 undoubtedly Jurassic in several of the eastern ridges of the Rocky Mountains, and 

 other districts of the far West. The rocks are, in general, a gray or whitish 

 marly or arenaceous limestone, with occasional pure compact limestone beds, 

 intercalated with laminated marls. The enormous Dinosauri, recently obtained 

 by Marsh and Cope from Colorado, are from the Jurassic. It is much less import- 

 ant here than in England, where it is subdivided into the Liassic, Oolytic and 

 Wealden. The name is derived from Mount Jura, in Switzerland. 



18. Cretaceous, The Cretaceous formation, along the Atlantic Coast and the 

 lower Mississippi Valley, consists of a series of beds of strata, differing from each 

 other ; but they are all earthy in form, consisting of beds of sand and sandy-clay, 

 except at a few points, where the strata have been cemented by oxide of iron into a 

 kind of sandstone, or conglomerate. In Texas it contains extensive beds of gypsum. 

 In New Jersey it produces the lower two beds of green-sand, called marl, which is 

 extensively used in agriculture, the value of which is due to the potash and phos- 

 phates which it contains. Ninety per cent, of it is a green silicate of iron and 

 potash, the rest being ordinary sand, and it contains no lime. But in Wyoming, 

 Utah, and Colorado, the Cretaceous attains a thickness of 9,000 feet, and its rocks 

 comprise beds of sand, marlite, clay, loosely aggregated shell-limestone, or rotten 

 limestone, and compact limestone. At the middle of the Cretaceous, lie the beds 

 of plastic-clay, outcropping across New Jersey, from Trenton to Amboy, and of 

 great importance to the fire-brick and pottery factories, as described in the Report 

 of Prof. Cook, of New Jersey, for 1876. 



The name Cretaceous is from the Latin word for chalk, the chalk of England 

 and Europe, being one of the rocks of this period ; but in this country it contains 

 no chalk, except in Western Kansas, 322 miles west of Kansas City, where a large 

 bed exists. It is within one mile of Trego station on the Kansas Pacific Railroad, 

 and is found over a tract 125 by 30 miles. 



The Cretaceous formation, in the far West, passes upwards into a coal-bearing 

 formation, several thousand feet thick, and covering on the upper Missouri River 

 not less than 100,000 square miles in the United States, besides the portion of the 

 belt extending into the British possessions. The area of other lignitic basin:-; 

 farther south, cannot be estimated, their width being unknown. Dr. Hayclen 



