AMERICAN GEOLOGY SURVEY UNDER WHEELER. 617 



regarded the primary features as due to folding-, the now evident 

 faulting being a phase of late Tertiary or post-Tertiary time." He 

 noted that the ranges were parallel, recurring at regular intervals and 

 of only moderate dimensions; further, that the ridges of the system 

 occupied loci of upheaval, and were not residua of denudation; and 

 that the valleys were not valleys of erosion, but mere intervals 

 between the lines of maximum uplift. 



He dwelt in considerable detail upon the phenomena of erosion by 

 wind-blown sand and silt-laden streams, and discussed the glacial 

 phenomena and the conditions attending the drying up of the great 

 inland lakes, applying the name Lake Bonneville, in honor of Captain 

 Bonneville, the explorer, to the great body of fresh water that once 

 occupied Sevier and Salt Lake valleys and of which the present bodies 

 of salt water, bearing these latter names are but the tiny residuals. 

 Those great bodies of water, which obviously could have existed only 

 under conditions of climate quite different from those of to-day, he 



Fig. 114. — Section of the Pahranagat range at Silver Canyon. (After G. K. Gilbert.) Scale, 1-72000. 

 Base line=level of Great Salt Lake. Q, Quartz Peak; S, Sanders Canon. 



believed to be coeval with the Glacial period of the northeastern States. 

 He found, however, no counterpart in this region of the general 

 glaciation of the eastern States, though there were local glaciers high 

 upon the flanks of the mountains. 



The abundant volcanic phenomena presented by the region were dis- 

 cussed in considerable detail and the recency of many of the lava flows 

 noted, the conclusions arrived at being to the effect that while "we 

 are not merely permitted to think of a renewal of that activity as pos- 

 sible * * '"' we are logically compelled to regard it as probable." 



The geological history of the basin region as read by Gilbert was to 

 the effect that the area was depressed below sea level from the close of 



a In Chapter VII of the volume on Mining Industry (Vol. Ill, Report, 40th Parallel 

 Survey, 1873) King refers incidentally to these mountains as the tops of folds whose 

 deep synclinal valleys are filled with Tertiary and Quaternary detritus. Just how 

 fully the problem may have been worked out in his own mind at that time is not 

 apparent, but in 1878, after the appearance of Gilbert's monograph, he expressed 

 the opinion noted above. The entire subject, it may be stated, was gone over by 

 J. E. Spurr in a paper read before the Geological Society of America in 1900 (see 

 Bull. Geol. Soc. Amer., XII, pp. 217-270), and the matter rediscussed at the winter 

 meeting of the same society in Washington in 1902. The prevailing opinions there 

 expressed were in accordance with the views put forward by Gilbert in 1875. 



