150 GEOLOGICAL SURVEY OF THE TERRITORIES. 



the smallest and most isolated of little collections of mica flakes, grad- 

 ually dying out more and more in approaching the central mass, afford 

 opportunity for a most accurate and careful study of the metamorphism 

 of bedded rocks into structureless granites of the most absorbing inter- 

 est. A few uncertain observations in the red granites near the south 

 border of the map may indicate that a southward dipping of the forma- 

 tion begins, and if such is the case, the eastern ridge of Evans may be 

 of an anticlinal structure, the mountain itself thus being at the inter- 

 section of an east-west and north-south fold, just as, topographically, it 

 lies near the intersection of a north-south and an east-west range of 

 mountains. About midway between the lower reaches of Clear Creek 

 and Bear Creek the rather obscurely-exposed granites show gneissic 

 areas, having invariably a high southern dip, or the reverse of the rocks 

 of the chief ridge and to the southeast of the same, indicating a north- 

 west and southeast synclinal, as shown on the map. This seems to first 

 appear in the canon through which Turkey Creek debouches from the 

 mountains, but here affected by one of the minor north and south, 

 folds, and from here on the course of the axis seems indicated at three 

 points, where the rocks were found having an abrupt change of strike, 

 the meaning of which was not at the time understood. What is thus 

 indicated of this axis would show it to dip to the northwest, but the 

 complimentary southeast dip that should occur does not seem to be in- 

 dicated, and its northern end is probably cut off" by a fault. 



The minor folds upon the Mount Evans anticlinal give to the greater 

 fold a squarish form, the northeast corner of which — that at Idaho — being 

 a sharp bend, while the northwest portion seems to be more rounded. 

 These two outer folds are the two principal components of the main 

 fold, and as the latter lies nearest the main axis of the range, it will 

 be mentioned first. From Clear Creek to Jam.es Peak no observa- 

 tions were made. At the latter the general strike of the gray-banded 

 gneissic schists forming the main ridge is northeast and north-northeast, 

 and dipping northwest from 25° to 45°. Following them along north- 

 eastward, however, they swing around more and more east to southeast 

 and in places nearly south, with rather low eastern dips, thus indicating 

 an anticlinal, having an axis lying just east of the main topographical 

 crest, and having a northward inclination. South Boulder Creek rises 

 at this point, and for nearly ten miles down its canon there seems to be 

 an uninterrupted series of schists and gneisses of different varieties, 

 some gray and some garnetiferous, striking more or less northwest- 

 southeast, with northeastern dip of 20° to 50°, till the stream enters an 

 apparently structureless granite mass, which will be referred to later. 

 Following northward along the range, the same swing of the strata 

 appears at the Boulder Pass, and again at Arapaho Peak. Through all 

 this distance, from Evans northward, would thus seem to be a great 

 anticlinal, with a northward-dipping axis, and if the series were unin- 

 terrupted, an enormous thickness of rocks must be represented. It is 

 quite possible, however, that unobserved faults occur, the northern side 

 being thrown upward, thus bringing the same series to view more than 

 once. A little north of Arapaho Peak the character changes some- 

 what ; some strikes from the northwest instead of from the southwest 

 •would seem to show that the axis of the anticlinal was nearly horizon- 

 tal, or rather had a gentle southward dip, as if an east-west synclinal 

 fold had flexed the north-south anticlinal fold. From Arapaho, and 

 from points northwest and southeast of the mountain, many fine views 

 of the great canon-cut mountain-mass at the north may be had, and the 

 structure generally shown is that of a broad flat anticlinal, with a nearly 



