302 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



numerous parallel fissures and corresponding mountainous upheavals, running- nearly 

 north and south. Of the latter, some consist of stratified rocks, others of stratified 

 rocks with a nucleus of igneous rocks, and still others, altogether, or nearly so, of 

 igneous rocks. Some of them extend continuously, with a considerable elevation, over 

 many miles to unknown distances, others fall off, and are succeeded by others, which 

 cannot be regarded as their immediate continuation, but are rather independent ranges 

 of similar character. 



An examination of the eruptive masses leads to the conclusion that, although 

 raised according to one system, the mountains cannot have been called into existence 

 by one great violent effort, but that their formation has occupied a considerable period, 

 probably with intervals of comparative rest ; also, that eruptive rocks, and conse- 

 quently considerable in equalities of the surface, existed long before the parallel ranges 

 were farmed. 



In the single mountain chains the forces frequently did not exhibit themselves uni- 

 formly along their whole axis, but acted witli locally more or less increased intensity 

 thus forming sporadic centers ot elevation, from which spurs run out in various direc- 

 tions across the valleys. Such sporadic upheavals are not confined to the principal 

 ranges, but are sometimes independently and irregularly interspersed between them, 

 has the general parallelism ot the ranges and valleys is not uniformly preserved, but 



ml, tins compoun 



d serrated mountain-system has been partially covered 



ind large inland s< 



-as (some of the more southern and lower portions per- 



ocean). The deti 



•itus from the mountains filled the valleys partially, form- 



•ustrine deposits, <n 



ed producing that peculiar shape which they now pre- 



le water has gradu 



ally receded, from causes of which we shall speak below 



country was less el 



levated, the lakes naturally covered a large area and the 



ded slower, bury] 



ng beneath the accumulating deposits the lower portion 



itains. In this ws 



lv only the tops or crests of the mountain ranges have 



nding out like isla 





Bland .Mountains:' 



a .u, loimmg wnat is now called Lost Mount- 



In this case, then, many of the intercepting barriers 



area, and from a n 



umber of separate valleys one main valley was formed. 



proportion henvee 



n the mountain masses, alone able to retain atmospheric 



d the bottomless 



accumulations of detritus in such districts, increases the 



; -enness of the COi 



mtry to a great extent, and makes it an absolute desert 



ffhapfl beginning in the C 



