THE BUILDING OF THE TUSHAR. 187 



been accomplished since the close of this second activity, though some of 

 the movement may, in the absence of evidence to the contrary, be assigned 

 to this period. 



The second period of cessation in the eruptions was broken at a com- 

 parativel}'" late epoch by a third outbreak at the northern end and at sev- 

 eral localities on the eastern flank in the vicinity of the faults. To this 

 third eruptive period belong the whitish rhyolite and the basalts, together 

 with several masses in the Sevier Valley which have emanated from the 

 foot of the range, and which will be discussed when we reach in regular 

 order the description of that valley. 



The history of the Tushar, therefore, comprises five tolerably distinct 

 periods since the commencement of the various activities which have 

 brought it to its present stage. 



Ist. An older eruptive ejjoch, building up an ancient volcanic mass. 



2d. A period of decay, in which the mass thus built was nearly leveled 

 down, and its fragments scattered far and wide and reconstructed in the 

 form of conglomerates and alluvial beds. . 



3d. A second eruptive period, more extensive than the first, rebuilding 

 the dilapidated mass. 



4th. A second cessation of eruptions and the introduction and progress 

 of extensive uplifting and faulting, accompanied by considerable erosion. 



5th. A third series of minor outbreaks of much smaller extent than 

 either of the others, some of which (around the bases of the range) are 

 very recent. 



In this history we perceive the combination of most of the important 

 forces and agencies of geology : eruption, displacement, erosion, and accu- 

 mulation ; all performing their parts in the general work, and yielding an 

 intelligible result in the erection of a grand uplift. 



