HISTORY OF DEVELOPMENT OP FAULT THEORY 261 



sumption of great horizontal diminution of the space covered by the disturbed 

 strata, and suggest lateral pressure as the immediate force concerned, while in the 

 Cordilleras the disi)lacement of comparatively rigid bodies of strata by vertical or 

 nearly vertical faults involves little horizontal diminution and suggests the appli- 

 cation of vertical pressure from below." 



The earlier and more prolonged work of the geologists of the Fortieth 

 Parallel survey had led them to conclusions different from Mr Gilbert's. 

 Mr Clarence King, writing in 1870 * said : 



"These low mountain chains which lie traced across the desert with a north- 

 and-south trend are ordinarily the tops of folds whose deep synclinal valleys are 

 filled with Tertjary and Quaternary detritus." 



Major J. W. Powell, in 1876, accepted, with some reservation, the 

 previously cited conclusions of Mr Gilbert. He described the struc- 

 tural characteristics of the Basin ranges as follows : f 



" The Basin province is characterized by north -and-south ranges that are mono- 

 clinal ridges of upheaval, and these monoclinal ridges are separated by stretches 

 of subaerial gravels that mask the structure of the areas of subsidence ; but while 

 this is the prevailing structure other types are found." 



The general acceptance of the fault theory appears to have influenced 

 Mr King's earlier conclusions, for in later writings, while maintaining 

 his earlier statement that the Basin ranges are a series of folds, he granted 

 the existence of abundant vertical faults and admitted the resultant dis- 

 location into blocks, as claimed by Gilbert and Powell. He wrote, in 

 1878, as follows: J 



"The frequency of these monoclinal blocks gives abundant warrant for the as- 

 sertions of Powell and Gilbert that the region is one prominently characterized by 

 vertical action ; yet when we come to examine with greater detail the structure 

 of the individual mountain ranges, it is seen 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 com- 

 plicated folds, riven in later time by a vast series of vertical displacements, which 

 have partly cleft the anticlinals down through their geological axes and partly cut 

 the old folds diagonally or perpendicularly to their axes." 



He concluded thus : § 



" 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, presumably 



* Geological Explorations of the Fortieth Parallel, vol. 1", 1870, p. 451. 

 f Geology of the Eastern Portion of the Uintah Mountaips, p. 29. 

 I Explorations of the Foi'tleth Parallel, vol. i, p. 735. 

 § Loc. cit., p. 744. 



UL 



