STRUCTURAL FEATURES. 209 



thickness of 1,300 feet as against 1,800 feet assigned to them in Nevada. 

 In the Canadian section the Devonian exposes only 1,500 feet of strata as 

 against 5,000 feet of Nevada limestone, but on the othei- hand the Carbon- 

 iferous limestone immediately overlying the Devonian exhibits a much 

 greater development than the corresponding horizon at Eureka. 



The sequence of strata in the Canadian localities shows a closer agree- 

 ment with the conditions of sedimentation at Eureka than do many expo- 

 sures of Paleozoic rocks situated but a comparatively short distance east- 

 ward of the latter area. In some respects the Canadian section more closely 

 resembles the Wasatch than it does the Eureka, as is shown in the great 

 thickness of Cambrian rocks below the Olenellus horizon. On the other 

 hand, there is no such development of Silurian and Devonian rocks in the 

 Wasatch as is shown both at Eureka and in Canada. Changes in sedi- 

 mentation appear much more sudden and varied in passing eastward from 

 Eureka than when followed northward. In structural and orographic 

 features the two regions present much in common, great lateral com- 

 pression, with anticlinal and synclinal folds, accompanied by north and 

 south lines of profound displacement. 



.STRUC'TUU.'VL FEATURE.S. 



For a clear understanding of the relation of the diiferent orogi*aphic 

 blocks to each other and to the numerous outbursts of igneous rocks, a 

 number of cross sections have been constructed across the central part of the 

 Eureka District. In one very mai-ked way these transverse sections across 

 the mountains are of more than ordinary interest, as they bring out the geo- 

 logical structure connecting a number of distinct and, at the same time, 

 interdependent mountain masses, whereas in most instances in the Great 

 Basin sections are th-awn across single uplifted ridges, isolated by broad 

 valleys whose recent deposits conceal everything beneath them. As these 

 valleys are frequently from 5 to 10 miles in width without rock exposures, 

 it is largely a matter of conjectui*e to say what the geological stnicture is 

 which underlies them. The most impressive orographic feature at Eureka 

 is the close relationship between the anticlinal and synclinal folds to the 

 north and south faults. It is these great meridional faults, at points attain- 



MON XX I'l 



