42 



ESTEEN UNITED STATES 



On reaching the footliills the train passes through a cut made in gray 

 massive limestone and red quart zose sandstone of the Casper forma- 

 tion, which incHnes steeply toward the east. Another aspect of this 

 fonnation may be seen to the left (south) of the railroad, where it 



erramte 



o 



■» 



On 



which 



right, the Casper fonnation is nearly horizontal and fonns the top of 



mesa 



hmestonc 



was 



This limestone is nearly pure calcium carbonate (98 per cent CaCOg), 



20 miles farther north, about 55,000 tons is 



Horse 



quarried every year to be Inii-ned for lime 'at the beet-suf^ar factories 



in eastern Colorado, where it is used m refinincr the sugar. 



FiGURF. 7.— Tertiary saud aiid gravel overlying the truncated eroded edge-s of o 

 approach to the Laramie Mountains between Cheyenne and Granite Cany 

 Pacifxc Railroad. 



Tlie ridge up wliich the train climbs in approach! 



remnant ot the broad plani that once extended unifonnlj 



moun 



prt'- 

 part 



streams have made 

 mountain rocks but have eroded 



Tertiary 



pi 



3 im- 

 large 



, leav- 



ing the ridge as the one practicable route by which the railroad can 



asccnc 



Tlie Tertiary sand^ and gravels of the , which coiL^ists of red sandstone, red sanJy 



train 



mountains form a tliin covering over ed<^es 



formations that rang 



Carhoniferoiis to Cretaceous. The edg 

 of the okler formatioris are truncated 

 that 19, the originally flat strata were 

 tilted and their edges cut off obliquely by 



Tertiary 



sliale, tlun beds of limestone, and thick 

 beds of gypsum. Uuconformably on this 

 lies the Sundance formation, consisting of 

 Bandatone and shale and containing 

 marine fossils that denote Jurassic age. 

 Tliis is followed with apparent conformity 

 by the Morrison forniation. which is noted 

 for its huge fossil reptiles. Upon the 



la d down upon them. Such a relation is Morrison, and apparently conformable 



called 



tngular unconformi 



urritude of these older rocks is know-n 

 from exposures in the valleys both north 

 and south of this ridge, and the relations 

 are shown in the accompanj-ing sketch 

 section (fig, 7). The oldest sedimentary 

 formation here is the Casper, consisting of 

 gray to white limestone and red sand- 

 stone. Next is the Chugwater formation. 



The , with it, Hes the Cloverly formation, con- 



sistm 



\^ - - ' -^ "-r^--^-^*^ tv/A^V^O tJ^L^dX tlt^UL ■-/ y 



shale. The upper sandstone is probably 

 equivalent in age to the Dakota sandstone 

 and is therefore the base of the Upper 

 Cretaceous series. Above the Cloverly 

 in conformable succession lie the Benton 

 shale, the Niobrara limestone, the Pierre 

 shale, and the Fn^ TTiTU >it^nr1^f.^Tio 



