CRETACEOUS PERIOD. 455 



The rocks comprise beds of sand, marly te, clay, loosely-aggregated 

 shell limestone, or " rotten limestone," and compact limestone. They 

 include in North America no chalk, excepting in western Kansas, 

 where, 350 miles west of Kansas City, a large bed exists. The Cre- 

 taceous limestones in Texas are firm and compact ; and some beds 

 contain hornstone distributed through them, like the flint through 

 the Chalk of England. 



The sandy layers predominate. They are of various colors, — white, 

 gray, reddish, dark green ; and, though sometimes solid, they are often 

 so loose that they may be rubbed to pieces in the hand, or worked 

 out by a pick and shovel. 



The dark-green sandy variety constitutes extensive layers, and goes 

 by the name of Green-sand ; and, as it is valuable for fertilizing pur- 

 poses, and is extensively dug for this object, it is called marl in New 

 Jersey and elsewhere. This Green-sand owes its peculiarities to a 

 green silicate of iron and potash, which forms the bulk of it, and 

 sometimes even 90 per cent., the rest being ordinary sand. There is 

 a trace of phosphate of lime, evidently derived from animal remains, — 

 as animal membranes and shells contain a small percentage of phos- 

 phates. Its value in agriculture is due to the potash and phosphates. 



Fossil shells are abundant in many of the arenaceous and marly 

 beds ; and in some they lie packed together in great numbers, as if 

 the sweepings of a beach, or the accumulations of a growing bed in 

 shallow waters, sometimes cemented together, but generally loose, so 

 as to be easily picked out by the fingers. 



The most northern outcrop of the Cretaceous observed on the Atlantic coast is in 

 New Jersey, just south of Sandy Hook. Mather suggested, in his " New York Geological 

 Report," that the formation underlies the sands of Long Island through its whole 

 length, on the ground that fossil shells and lignite have been found in digging wells, 

 and other excavations; but, as he had seen none of the shells, the evidence thu3 far 

 published is as good for the existence of Tertiary beds as for Cretaceous. 



The inner limit of the Cretaceous formation, on the Atlantic border (see map, p. 144), 

 follows a line across New Jersey, from Staten Island to the head of Delaware Bay; 

 across Delaware to the Chesapeake; across Maryland, between Annapolis and Balti- 

 more, southwest into Virginia. The formation occurs at Elizabeth on Cape Fear River, 

 in North Carolina, and sparingly in South Carolina. But, more to the westward, at 

 Macon, Georgia, commences the large Southern Cretaceous region, which is continued 

 into the Mississippi basin, and whose inner outline passes by Columbus in Georgia, 

 Montgomery in Alabama, and then bends northward over northeastern Mississippi 

 across Tennessee, just west of the Tennessee River, toward the mouth of the Ohio; it 

 outcrops southward on the west side of the Mississippi over eastern Arkansas, spread- 

 ing at the same time westward, south of Little Rock and Fort Washita. Not far from 

 the last point, the Cretaceous area expands southward over part of Texas; also north- 

 ward, covering part of the western border of Iowa and Minnesota, and continuing on 

 in the same direction, beyond the northern boundary of the United States, into British 

 America. It also spreads over a large part of the eastern slope and the summit region 

 of the Rocky Mountains, as already mentioned. West of the summit, it extends over 

 much of the valley of the Colorado, to the meridian of 113° W. In California, the Cre- 



