148 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



not itself directly traced. Descending from The Cliief northward, thus 

 crossing the edges of the steeply upturned schists and ascending through 

 the formation, but at the same time following somewhat along it north- 

 ward, it is found to swing more and more northward, and then — near a 

 iiorth and south line passing through Idaho — to bend directly around to 

 a southwest strike and northwest dip. It is a sharply-folded anticlinal 

 dipping steeply northward. Still following along the strata, they again 

 swing northwest and again southwest, showing a similar abrupt fold. 

 Following up Clear Creek from Idaho, a number of such folds occur, the 

 dip of the irregular schist and gneiss rocks being invariably east, north, 

 or west, but never south until, near the head- waters of that stream, a 

 more constant southwest strike is attained, with northwest dip, as finely 

 shown in the Gray and Torrey Peaks, and north and east of the same. 

 Thus regarded all together, the Evans mass appears as a broad anticli- 

 nal, with its axis dipping northward, and carrying on its face a number 

 of minor crumjjles, smaller anticlinals and synclinals, like ripples on the 

 greater wave of rock, Naturally these smaller folds render the more 

 general geology very confused. This seems to be particularly the case 

 near Idaho, but many observations showed the same little folds running 

 for considerable distances. The smaller valleys here show some pecu- 

 liar relations between topography and geology, sometimes following the 

 softer beds in their sinuosities for considerable distances. The numerous 

 minor anticlinals and synclinals here observed are indicated by their 

 proper symbols. The schists and gneisses appear well exposed ia the 

 lower portions of Chicago Creek, but higher up granites begin to pre- 

 vail, very abrupt transitions from one to the other being frequent. 

 Starting from the eastern base of the Gray and Torrey Peaks, and curv- 

 ing around northward, is a most profound and regular glacier-carved 

 gorge, with sweeping precipitous sides towering up on the east side to 

 the rather even-topped summit of MacLellan Eidge. On the west side, 

 plainly noticeable in Gray and Torrey, the handsome gray and rather 

 evenly banded gneisses dip rather steeply to the west and north, while 

 just opposite, on the east side, an opposite dip occurs, the saddle 'just 

 east of the two peaks being in a sharp anticlinal axis. Opposite the 

 mountain, and a little south, perched midway up the precipitous face of 

 the MacLellan Eidge, its houses held on to the face of rock by chains 

 and rods, and accessible only by the aid of ropes, is the Stevens mine. 

 Here some structureless granite masses confuse the gray gneiss, the mine 

 being in one of them, and faults occur, but it seems to be here that the 

 axis of the anticlinal leaves the valley, for down the latter the general 

 dip is to the northwest. Joining the next fork, the strike still bears east 

 and west, or northeast and southwest, dipping north and west, till about 

 midway to Georgetown, when a mass of hard, structureless, massive, 

 porphyritic granite is met, in which the Terrible mine is situated. The 

 contact between the schists and granites can be quite readily traced up 

 the steep northern slope of the valley just west of the mine, and is mostly 

 very abrupt. The ends of the westward-dipping schists mostly lie up 

 against the granite, but in places bend down into it, being much con- 

 torted, and while the line of contact is often remarkably well defined, 

 the change from one to the other being instantaneous, yet in places the 

 change is less abrupt, the irregular ends of the schist-bands being ap- 

 parently absorbed in the granite mass. Some inclosed patches of schist 

 appeared in the granite, but with no recognizable general arrangement, 

 while below the structureless granite a southeast dip appeared, intimat- 

 ing that the granite occupied an anticlinal axis, probably the northern 

 cantiniiation of the Gray's Peak anticliual, as indicated on the map. 



