44 ANNALS NEW YORK ACADEMY OF SCIENCES 



Las Vegas. The main line of outcrops then swings northeastward to a 

 point 15 miles or so southwest of Clayton. The outcrops along the moun- 

 tain front in Colorado and New Mexico occur in hog-backs. The north- 

 east-southwest line of surface occurrence in New Mexico is an irregular 

 cliif. The lines of outcrops are not completely continuous. At Golden 

 the Morrison has been crowded out by igneous action, and at Manitou and 

 other places it has disappeared through faulting. Outcrops also occur in 

 the canyons of the Purgatory, Apishapa and other rivers in Colorado, and 

 of the Cimarron in New Mexico and Oklahoma. 



A. E. Marvine (1874, 3), in the seventh Annual Report of the II. S. 

 Geological and Geographical Survey of the Territories, describes the 

 "Jurassic" or the beds overlying the red series of supposed Triassic age 

 as follows : 



"General char act ers.^The series of strata lying next above the red 

 beds form a group of rocks in which the thin-bedded and shaly element 

 decidedly predominates. The outcropping edges of these beds have there- 

 fore generally been more eroded away than the harder beds above and 

 below, so that. they generally appear in valleys; and being soil covered, 

 they are not usually well exposed. 



"The arenaceous element still predominates, though argillaceous mate- 

 rial is often present to a very large extent, while beds of impure limestone 

 occiir — one of which appears very persistent — and gypsum is frequent in 

 thin layers, and sometimes occurs in Avorkable quantities and of good 

 quality. As before, red is the prevailing color, though a series of marked 

 variegated shales occur, and weathering frequently produces an ashen- 

 gray tint upon the surface. . . ." 



Some of these beds are probably of lower horizon than the true Morri- 

 son. 



The following description of the Morrison formation east of the Rocky 

 Mountain front is given by Darton (1901:, 8) : "Its general character is 

 nearly uniform throughout, a series of light-colored, massive clays, 'joint 

 clays,' with thin beds of limestone and sandstone of fresh-water origin 

 containing bones of saurians of the so-called 'Atlantosaurus' fauna. Its 

 thickness averages less than 200 feet in most cases. It presents frequent 

 and rapid variations in the local succession of beds, but the predominance 

 of joint clays of chalky aspect and the occurrence of maroon and purplish 

 layers among them are characteristic features." Lee speaks of the Morri- 

 son as "uniformly variable," a term especially applicable. 



In the extreme northern part of Colorado the ]\Iorrison is said to rest 

 upon the marine Sundance beds. Throughout most of the northern Colo- 

 rado area it rests upon the red beds of the Chugwater formation. Fur- 



