HISTOKY OF DEVELOPMENT OF FAULT THEORY 263 



across the map of the Great basin an east-and-west line touching the soutliern end 

 of Great Salt lake, it will intersect not less than twenty lines of profound displace- 

 ment. Farther south, in the latitude of Sevier lake, the number of orographic 

 blocks into which the country has been broken is even greater. 



"As already stated, that part of the Great basin lying north of the Nevada-Oregon 

 boundary has the same pronounced orographic structure as the main area of in- 

 terior drainage. In considering the physical history of the Great basin as a whole, 

 however, we find over a wide area two distinct types of structure belonging to 

 widely separated periods and due to forces acting in different directions. During 

 the first period the rocks were plicated and crumpled into anticlinal and synclinal 

 folds, and at the time of the second disturbance the present topography, due to 

 orographic displacement, was initiated. These two periods of orographic move- 

 ment were recognized by Mr King, who speaks of the Great basin as a ' region of 

 enormous and complicated folds, riven in later times by a vast series of vertical 

 displacements.' ^ 



" These two types of structure are apparent at many localities throughout the 

 central portion of the region of interior drainage, but immediately north of the 

 Nevada-Oregon boundary, where the rocks are almost entirely volcanic, we find 

 only such disturbances as are due to faulting. The age of the volcanic beds in the 

 northern extremity of the Great basin would, therefore, seem to be intermediate 

 between the two periods of disturbance." 



In subsequent papers Mr Russell reiterated these conclusions. In 

 1886 Mr J. S. Diller extended the application of the fault hypothesis to 

 the Sierra Nevada. He remarks : t 



** Structurally the Sierra is like the Great Basin range, differing chiefly in the 

 magnitude and in the present elevation of the blocks. Like the orographic blocks 

 of the Great Basin area, they are composed of plicated strata, the folding of 

 M^hich, as has been pointed out b}'^ a number of observers, took place long before 

 the faulting that gave birth to the peculiar features of the ranges. It is important 

 to remember the fact that at the time the strata of which the Sierra Nevada range 

 is composed were folded — i. e., about the limits between the Jurassic and Creta- 

 ceous periods — the Sierra Nevada range was not differentiated from the continental 

 mass of the Great Basin region, and it was not until a very much later period that 

 this separation occurred." 



In a paper published the succeeding year he wrote as follows : X 



"The plication of the strata in the Sierra Nevada range took place, at least in 

 great part, about the close of the Jurassic or beginning of the Cretaceous period, 

 but the faulting which really gave birth to the Sierra as a separate and distinct 

 range by differentiating it from the great platform stretching eastward into the 

 Great Basin region did not take place until toward the close of the Tertiary or 

 the beginning of the Quaternary. 



'►'Although the faulting may have commenced earlier, the greater portion of the 



* U. S. Geological Explorations of the Fortieth Parallel, vol. i, p. 735. 

 tBull. U. S. Geol. Survey, no. 33, p. 15. 

 X Bull. Phil. Soc. Wash., 1SS7, vol. ix, p. 4. 



