GEOL.-VOL. I.] TURNER— ORIGIN OF YOSEMITE VALLEY. 263 



and ridges of the Great Basin are the result of displace- 

 ments along normal faults of sections of this broad arch 

 Gilbert^ was, however, the first to elucidate the structure 

 of the Basin Ranges. He found Httle evidence, except in 

 the Inyo Mountains and the Sierra Nevada, that there had 

 previously been a period in which the rocks had been 

 folded and crushed and ranges formed by lateral pressure. 

 It is, however, possible that such ranges are much more 

 abundant in the fortieth parallel region than in the districts 

 to the south, where most of Mr. Gilbert's observations were 

 made. Clarence King- apparently states the case fairly for 

 the fortieth parallel belt as follows: — 



The frequency of these mouoclinal detached blocks gives abundant war- 

 rant for the assertions of Powell and Gilbert, that the region is one promi- 

 nently characterized by vertical action; yet when we come to examine with 

 greater detail the structure of the individual mountain ranges, it has seemed 

 that this vertical dislocation took place after the whole area was compressed 

 into a great region of anticlinals with intermediate synclinals. In other 

 words, it was a region of enormous and complicated folds, riven in later time 

 by a vast series of verdcal displacements which have partly cleft the anti- 

 clinals down through their geological axes and partly cut the old folds diago- 

 nally or perpendicularly to their axes. 



The Sierra Nevada and some of the ranges of the Great 

 Basin thus appear to have had a common orogenic history. 



So much has been written about the normal faults of the 

 Great Basin that extended discussion of them here is unnec- 

 essary. There is, however, some difference of opinion as 

 to the amount of this faulting and the time at which the 

 main faults were formed. The greatest fault-scarp of the 

 region under discussion is probably that of the east face of 

 the Sierra Nevada. This scarp is supposed by Le Conte ^ 

 to have been formed at the close of the Tertiary. Lind- 

 gren^ thinks that the first faulting separating the Sierra 

 Nevada from the interior basin occurred before the depo- 

 sition of Chico-Cretaceous, but supposes that vigorous 

 faulting occurred along the same fracture at various times 



1 wheeler Survey Reports, Vol. Ill, 1875, PP- 21-42. 



2 Fortieth Parallel Reports, Vol. I, 1878, p. 735. See, also, Russell, Monograph XI, U. S 

 Geol. Surv. on L,ake lyahoutan, 1885, p. 26. 



^University Chronicle, Berkeley, California, Vol. I, 1898, p. 481. 

 <Journ. Geol. Vol. IV, 1S96, p. S94. 



