MESOZOIC TIME CRETACEOUS. 829 



Ischyrosaurus antiquus, both described by Leidy in 1873. Nothing of the 

 Laramie is recognized in Kansas. 



The Reptiles and other fossils in the beds referred to as Upper Laramie 

 indicate not only their Cretaceous age, but also their close relations to the 

 Lower Laramie. At present the line between the two divisions cannot be 

 definitely drawn. 



The subdivisions of the Rocky Mountain Cretaceous, including the Laramie, were first 

 described by Hayden and Meek. Their papers commenced in 1856, and appeared at inter- 

 vals for 20 years. Meek's Report on the fossils, in which the stratification is reviewed, 

 constitutes vol. ix. of the Reports of the Hayden Expedition (1876). Their subdivisions 

 were the Dakota, Fort Benton, Niobrara, Fort Pierre, and Fox Hills. The Tertiary sec- 

 tion in the "Upper Missouri region," described by Meek and Hayden, contained 

 (1) Dakota group, 400' ; (2) Fort Benton, 800' ; (3) Niobrara, 200' ; (4) Fort Pierre, 700' 

 and (5) Fox Hills, 500'. G. H. Eldridge in 1889 grouped the divisions into tlie three 



(1) Dakota; (2) Colorado, and (3) Montana. C. A. "White had earlier recognized (1876) 

 the same grouping under the names Dakota, Colorado, and Fox Hills. 



The Colorado formation and its relations to the other divisions of the Cretaceous have 

 been reviewed in detail by T. W. Stanton ; and from his report of 1893 many of the follow- 

 ing facts are taken. The thickness of the Upper Cretaceous series at the Black Hills is 

 less than 1000' : (1) the Dakota, 250'-400' ; (2) the Colorado, 300'-500' ; (3) the Montana, 

 150'-350' (H. Newton). In Cinnabar Mountain, Montana, the total thickness, according 

 to Weed, is about 4300' : (1) the Dakota, 526' ; (2, 3) the Colorado and Montana, 2850' ; 

 (4) the Laramie, 935'. East of the Front Range, in Colorado, the Dakota outcrops at the 

 base of the range, and, outside of this, the other later groups in succession, as first shown 

 by MarATine. In the Denver region there are : (1) Dakota, 300' ; (2) Colorado, 1100', of 

 which 400 is Fort Benton and 700 Niobrara ; (3) Montana, 8700', of which the Fort Pierre, 

 7700', and Fox Hills, 800'-1000' ; (4) the Laramie with the Denver group, 2000'. The 

 thickness diminishes southward, and between Canon City and Pueblo, on the Arkansas 

 River, the Montana group is but 3000' thick. The section at Coalville, in Utah, according 

 to Stanton, which is peculiar in containing a great coal-bed in the Colorado portion, con- 

 sists as follows: (1) Dakota, 5000'?; (2) Colorado, 1560'-1660', mostly sandstone and 

 fossiliferous, but with a heavy bed of coal at the top of the lower stratum of 500' to 600' ; 

 (3) Montana, about 2900', of sandstone and shales, with probably 1500' of beds above ; 

 and in the part referred to the Montana group on account of the marine fossils, there are 

 some thin plant beds, the fossil plants of which are in part Laramie. 



The Kansas Cretaceous consists, according to S. W. Williston, of 350' to 400' of 

 Dakota beds, 300' to 400' of overlying shales and limestone of the Benton gi'oup, and 400' 

 to 450' of chalk and other beds of the Niobrara, making the Colorado series 700' to 850' 

 in thickness ; and above these, 50' to 100' of beds of the Montana group. The Laramie 

 is absent, the next beds above being those of the Loup Fork Miocene Tertiary. 



Newberry divided the Cretaceous of New Mexico into : (1) Dakota, 250' to 400' ; 



(2) Colorado, 1200' to 1.500' ; and (3) Montana, 1500', part of the Laramie being here 

 probably included. (Macomb's Expl.Exp., with a review by Newberry of the conclusions 

 he presented in Lieutenant Ives's Rep. on the Colorado River of the West.) 



The age of the Laramie beds (or the Lignitic, as they were called), whether Tertiary 

 or Cretaceous, was left undecided by Meek in his report of 1870. To the Lignitic horizon 

 he referred the Judith Biver group, occurring at the mouth of Judith River in Montana, 

 having there a thickness of about 415' and consisting, beginning below, of sands and clays 

 with Unio, 100' ; impure lignite, 25' ; sand and clay-beds with shells and Dinosaurian 

 remains, 100' ; sand and clay, 100' ; impure lignite with Ostrea, 10' ; sandy marl with some 

 lignite and species of Ostrea, Corbicula (3 species), Goniobasis, salt-water species, 80'. 



