EOUTE COUNCIL BLUFFS TO OGDEN. 



63 



sight also north of Grenvillc, 



miles 



mountains 



flank. 

 Range, 



These are the Ferris Mountains, Jying just west of the Seminoe 

 The white .scallops are vertical beds of limestone which 

 have resisted erosion while the softer beds around them have been 



worn away 



mount 



name 



many 



South of Grenville the rocks, which have been domed, are eroded 

 so deeply that the Mowry shale is exposed at the surface in the center 

 of the dome and the several sandstones of the Frontier formation lie 

 in concentric ridges arotmd it. The shale between these sandstones 

 contains hmestone concretions in which are shark teeth, ammonites, 

 scaphites, and other fossils of marine animals that indicate Upper 

 Cretaceous (Benton) age. These sandstones contain oil in some 

 places, and for the purpose of ascertauiing their depth south of 

 Rawlins, where a well was started near the base of the Mesaverde 



formation 



t^ c? 



measured 



south of Grenville, where it was found that the sandstone lies 2,200 

 feet below the lowest sandstone ledge of the transitional zone between 

 the Mesaverde and the Steele shale. The shale between the base of 



somewhat more 



2,200 feet thick. 



A few miles east of Rawlins the outcropping edges of the several 

 formations are passed over in rapid succession. These strata are 

 upturned around the Rawlins dome ^ and range in age from Cam- 

 brian up to Cretaceous. (See table on p, 2.) Some of these for- 



mations 



From the 



geologist's point of vie^v 



o 



inevitable 



railroads are built where the easiest grades can be obtained rather 



^ The center of the Rawlins uplift con- 

 sists of granite which reaches an altitude 

 of more than 7,600 feet in the hills north of 

 the railroad, Aronnd thisgranite core and 

 sloping away from it are the sedimentary- 

 rocks. The oldest, the Cambrian quartz- 

 ite, is very hard and forms conspicuous 

 slopes. The railroad is built through a 

 narrow gap in these rocks west of Raw- 

 lins. (SeePI. Xin,.!, p.61.) The Car- 

 boniferous limestone lies in G:eneral uncon- 

 formably on the Cambrian qiiartzite, but 

 is separated from it in some places by 

 beds of iron ore. Red sedimentary rocks 

 that lie above this limestone are separated 

 into two parts by a layer of similar lime- 



stone. It is possible that the upper part 

 represents the Chugwater red beds and 

 the lower part the Casper formation of 

 the Laramie region. 



The Sundance formation comes next, 

 with its characteristic marine Jurassic fos- 

 sils, and above it lie the variegated Mor- 

 rison beds. These are succeeded by the 

 Cloverly, which here, as elsewhere, con- 

 sists of two sandstones, the lower one con- 

 glomeratic, separated by dark shale. 

 Above the upper sandstone is the Mowry 

 shale, the sandstone of the Frontier for- 

 mation, and a body of shale which in- 

 cludes equivalents of the Steele shale 

 and the Niobrara formation. 



