68 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



distance. So liere, too, we find a large number of extensive displace- 

 ments. Enormous fragments have been broken from the main mass and 

 have been thrown into regions where they appear, from their relations 

 to surroundings, as total strangers. Some portions have been plicated 

 and overturned, i)resenting features of structure and texture that are 

 entirely at variance with those of the vicinity. 



Elhninating such occurrences, we may, from the standpoint of a stra- 

 tigraphist, regard the main chain of the Wind Eiver Mountains as a steep, 

 anticHnal range, a portion of the anticUnal fold being obscured. It will 

 be seen that the remaining portions of the range corroborate this view. 



Passing over the "belt" of schistoid rocks on the eastern slope of the 

 main chain, we once more enter a granitic area within the foot-hills. 

 Although resembling, to a certain degree, the granites farther west, we 

 here find decided differences. Perhaps the most striking is the well- 

 developed structure. On the higher portions of the foot-hills this is not 

 so noticeable, as their exposed i)osition has necessarily caused serious 

 disturbance of the integrity of the stratoid masses. At such points they 

 are thoroughly broken, partly by virtue of the prominence of original 

 planes of deposition, partly on account of transverse joints. As we 

 descend along the ridges, however, we find the character of this granite 

 well exhibited. Frequently quite considerable areas can be seen where 

 the bare rock is exposed. There we note the more or less clearly defined 

 stratification, which is evident at a glance. We find that the strata of 

 granite retain their easterly dij), which gradually assumes a lower angle 

 (from the horizontal). This even slope becomes more prominent as we 

 approach the area of unchanged sedimentary beds. An interesljing oc- 

 currence may be observed in this connection. High up in the foot-hills 

 the granite resembles that of the main chain in lithological character. 

 It is generally gray to light brown, contains orthoclase, oligoclase, quartz, 

 and muscovite. Accessory minerals consisting of amj)hibolite, chlorite, 

 and — rarely — corundum are found there. Near the eastern base of the 

 foot-hills the first sedimentary beds consist of red quartzites. They bear 

 ample evidence of having been metamorinhosed. Immediately below 

 these quartzites we find regular, well-defined strata of reddish and red 

 granite. It is coarser grained than high up in the hills, and contains but 

 very Uttle oligoclase. From the appearance of the ridges it is evident 

 that large masses of sedimentaries, once covering them, have been re- 

 moved. Erosion xirogressed to such a depth that the hard granites were 

 reached, and these now lie exposed upon the surface. At some localities 

 it seems very difficult, indeed, to determine where the granite ends and 

 the red quartzite begins. The latter frequently extends in tongue-shaped 

 masses ux) on slopes of the ridges, while they are cut away in the valleys 

 and canons. At both of these places the junction-line between the two 

 is sometimes very much obscured. Above the quartzites we have un- 

 changed sedimentary beds. 



From these observations we are enabled to say, with certainty, that 

 the seat of metamorx)hosing influences was removed in a direction from 

 the third chain toward the main longitudinal axis of the range. It may 

 further be said that the direction along which these influences exerted 

 their force is determined by lines rectangular to the trend of the third 

 chain and its scattered continuations. 



As we follow the foot-hills in their southeasterly coiu-se, we reach a 

 point from where they branch off to the eastward. The continuity of 

 the chain is somewhat broken here, but it can readily be traced, more 

 particularly by the aid of the sedimentary beds. In this deflection it 

 remains xJarallel with the range. If we examine the conditions existing 



