TE COUNCIL BLUFFS TO OGDEX. 51 



massive sandstone of the Mesaverde formation that lies on it. These 

 transition rocks become gradually more sandy toward the west, and 

 west of Rawlins they form a part of the Mesaverde formation. 



Pine Ridge is the divide between the Laramie River drainage and 

 that of Rock River. The waters of its eastern slope pass eastward 

 through the Laramie Mountains and enter Platte River at Fort 

 Laramie, 80 miles to the northeast. Those of the western slope flow 

 tln-ough Ropk River and Medicine Bow River to the Phitte and thence 

 through the Semuioc ^fountains around the north end of the Laramie 

 Mountains and after a circuitous route of about 250 miles join those 

 of the eastern slope at Fort Laramie. 



Just before reaching Rock River station the train crosses the river 



& 



of the same name, and good exposures of the Steele 



Rock River. g^^^i^ ^^^^ ^^ ^^^^ -^ ^^^ ^^^^ ^^ ^^ic north bank. 



Po''^ldSon^^ Northwest of the town the railroad passes over a 



Omaha 612 miles. broad plaiii formed on this soft shale. 



About 10 miles from Rock River the road crosses a 

 low^ sharp hogback of Xiobrara limestone. This chalkj-white bed^ 

 5 to 10 feet thick, forms a crest because it is harder than the shale 

 above and below it. 



Ridge takes its name from tli-e prominent hogback ridge north of 

 the station, formed by a hard sandstone in the Benton shale. The 



railroad parallels tliis ridge for a mile or more and then 

 Ridge. ^^^g through it west of the station. The lower part of 



Elevation 6,692 feet, the Bcntoii shalc is well exposed north of this sand- 



miles 



clung of the strata, 't'l 



ge, in the center of the anticline formed 



a mQe before recrossing the sandstone and the Niobrara limestone and 



finally returns to the Steele shale in the northern limb of the arch. 



Near Ridge the sandstone disappears because the fold that extends 



westward from the Laramie Range here plunges beneath the surface. 



which 



formation 



glomeratic portion of which forms the crest of the bluff because of its 

 superior hardness and forms also the long southward slope seen to the 

 right from the train. Underneath this cono:lomerate occiu- in descend- 

 ing order the pink and blue shales of the Morrison formation, which, 

 because of the numerous shadesof color, are often called the variegated 

 beds; the Sundance formation, containing numerous vertebrate and 

 invertebrate fossils which" prove its Jurassic age; and the Chugwater 

 red beds. 



The Morrison formation is probably the most interesting of those 

 exposed here, because of the fossil bones of huge reptiles that it con- 

 tains. The dinosaurs are described below by C. W. Gilmore, of the 



