PALEOZOIC TIME — CARBONIC. 733 



erous rocks appear to have been followed by the Mesozoic without extensive 

 intervening upturnings in the region of the Wasatch and through the whole 

 length of the mountains, from western Texas and Mexico to the Arctic Seas. 



But west of the Wasatch belt, in the mountain ridges of the Great Basin to 

 the meridian of 117|-° W., according to King, Carboniferous limestone is to a 

 considerable extent the surface rock, there being no overlying Mesozoic strata ; 

 and this limestone and the older Paleozoic formations are flexed and faulted 

 in mountain-making style. The time of the upturning is uncertain because 

 of the absence of later beds except over the region beyond the meridian 

 of 117-|-°. But, as King implies, it took place probably at the close of 

 the Paleozoic. 



The Eureka Mountains in the Great Basin (near 116° W. and 39^ N.), described by- 

 Arnold Hague (Geol. of the Eureka District, JJ. 8. G. 8. 3Iemoirs, 4to, vol. xx., 1892), 

 are one of the mountain groups of eastern Nevada, which probably was upturned at this 

 time. The prominent ridges, which were produced largely by faults and uplifts (their 

 maximum displacement 13,000') , are : the Prospect Ridges, consisting of Cambrian and 

 Silurian rocks ; the Fish Creek Mountains, Silurian ; the Silverado and Country Peak, Silu- 

 rian and Devonian ; Diamond Mountain, Devonian and Carboniferous ; Carbon Ridge and 

 Spring Hill, Carboniferous. The thicknfess of the formations, as deduced from several sec- 

 tions, according to Hague and Walcott, is as follows : Cambrian, 7700' ; Silurian, 5000' ; 

 Devonian, 8000'; Carboniferous, 9300', — in all 30,000'. This great thickness indicates, 

 as Hague suggests, that a pi'ofound geosyncline north and south in trend was here made. 

 The Eureka, Carboniferous, Devonian, and Silurian beds have been traced from the Eureka 

 district westward to that of the Pinon Range, which is an indication that the latter range 

 participated in the geosyncline. How far north the belt extends remains to be ascertained. 

 The Archaean ridge of the East Humboldt Mountains stands to the east and north of the 

 Eureka Range. 



The Eureka geosyncline was wholly independent of that of the Wasatch, as shown by 

 the thicknesses of the several Paleozoic formations occurring in the two ; for the thick- 

 ness of the Silurian of the Wasatch is only 1000', of the Devonian, 2400', while that of the 

 Carboniferous is 14,000'. Whether the Silurian unconformability in the Eureka region 

 between the Lone Mountain limestone and the underlying quartzyte is a result of an 

 upturning at the close of the Lower Silurian, or of later faulting, does not appear to be 

 determined by the observed facts. 



UPTURNINGS IN FOREIGN COUNTRIES. 



Regions of upturned rocks are the only kind in which there is good reason 

 to look for unconformabilities. Through the course of Paleozoic time in 

 Europe, disturbances appear to have been more frequent than in America. 

 But they were inferior in extent to those at its close. Murchison remarks 

 that the close of the Carboniferous period was specially marked by disturb- 

 ances and upliftings. He states that it was then " that the coal strata and 

 their antecedent formations were very generally broken up, and thrown, by 

 grand upheavals, into separate basins, "which were fractured by number- 

 less powerful dislocations." In the north of England, as first shown by 

 Sedgwick, and also near Bristol, and in the southeastern part of the Coal- 

 measures of South Wales, there is distinct unconformability between the 



