HOLMES.] SUMMARY. 71 



It seems to owe its present couformation to tlie occurrence of three 

 nearly parallel lines or belts of displacement, two of depression and one 

 of elevation. 



The depression along the valley of Eoaring Fork, which has already 

 been presented in Fig. 1, is included between the diverging axes of the 

 two ranges, and exhibits some very curious examples of faulting and 

 folding. 



The elevated belt, which constitutes the range, is about forty miles in 

 length. It slopes gently toward the depression on the east, but drops oif 

 very abruptly on the west in a great fault-fold. Four considerable areas 

 of eruptive granite occur along the axis of this belt or zone, and the de- 

 pressions between these contain synclinal folds of the sedimentary beds, 

 as seen in the longitudinal section given on the large sheet. 



It will be 'noticed, by reference to the transverse sections, that the 

 axis section, which follows approximately the crests of the range, is 

 generally to the east of the axis of displacement. The reason of this 

 ^ will be plain, when it is observed that the entire series of strata rise 

 gradually from the valley of the Eoaring Fork synclinal, until the axis 

 of displacement is reached, and that the highest points, which would at 

 first stand along the line of this axis, are now carried back by erosion 

 from one to five miles to the east. 



The amount of vertical displacement along the fault-fold, between 

 Aspen Creek on the northwest, and station 3 on the southeast, does 

 not fall short of 5,000 feet at any point, and will probably measure 10,000 

 feet in one or two places along the west side of the Snow Mass group. 



The depressed belt west of the range, occupied by the valleys of Eock 

 Creek and East Eiver, is very intimately associated with the fault-fold, 

 and has been produced by the downthrow on that side rather than 

 by any independent folding, as the strata do not rise at all to the west, 

 except for a few miles along the east face of Treasury Mountain, as seen 

 In sections E and F. 



On the 11th day of September we fell in with the main party just south 

 of Italien Mountain, and after spending a few days in the review of the 

 geology about the headwaters of East Eiver, began our return march to 

 the East. 



