292 G. D. LOUDERBACK — STRUCTURE OF THE HUMBOLDT REGION 



of mountain origin, described the formation of mountains by the tilting 

 of faulted blocks as the " Basin Range type." 



This view of the origin of the ranges of the Great basin was accepted 

 more or less completely by the other geologists who later worked in that 

 field. In particular, I. C. Russell, during his investigations into the his- 

 tory of lake Lahontan, made observations on the mountain ranges of 

 western Nevada and adjoining territory, which convinced him of the 

 persistence of this type of mountain structure throughout the Western 

 Basin region. In his monograph on lake Lahontan he publishes a 

 map* showing the position of the fault lines along which the blocks 

 were raised or depressed to form the ranges. He also shows by another 

 map, and by a plate,f the lines along which he has observed evidences 

 of Recent faulting. As these Recent fault lines coincide with the lines 

 of earlier faulting, he regards them as indicating a continuation of the 

 earlier movements along the same lines in Recent time. The forces may 

 be active even now. 



The geologists of the Fortieth Parallel Survey had originally believed 

 that the ranges were formed by folding and were " ordinarily the tops of 

 folds whose deep synclinal valleys are filled with Tertiary and Quater- 

 nary detritus." J But after the publication of the views of Gilbert and of 

 Powell, King accepted the idea of monoclinal blocks formed by faulting 

 as a prominent characteristic of the Basin region, but at the same time he 

 insisted on the importance of the folding of the region by lateral com- 

 pression. He says : § 



" The geological province of the Great basin, therefore, is one which has suffered 

 two different types of dynamic action: one, in which the chief factor evidently 

 was tangential compression, which resulted in contraction and plication, presuma- 

 bly in post-Jurassictime ; the other, of strictly vertical action, presumably within 

 the Tertiary, in which there are few evidences or traces of tangential compression." 



Russell and other later workers also recognized these two types of 

 structure in the Great basin — the " enormous and complicated folds, 

 riven in later times by a vast series of vertical displacements." || 



Professor Le Conte presented an interesting general conception of the 

 genetic relations of these ranges. The Great Basin region, most, perhaps 

 all, of which was under the water of the ocean during Paleozoic or Meso- 

 zoic time, has been elevated as a whole in such a way that the higher 

 peaks, notwithstanding erosion on a great scale, are from 10,000 to 15,000 

 feet, and even the broad valleys of its northern part are from four to six 



*U. S. Geol. Survey, Monograph xi, plate iii. 



t Ibid., plates xliv and xlv. 



X U. S. Geo). Exploration of the Fortieth Parallel (Fortieth Parallel Survey), vol. iii (1870), p. 451. 



g Fortieth Parallel Survey, vol. i (1878), p. 735. 



|| King : Fortieth Parallel Survey, loc. cit. 



