54 GEOLOGICAL SURVEY OF THE TEREITORIES. 



gorge begins, there is a sort of natural bridge. The stream has 

 worn a narrow channel through the rocks. At the summit the gorge 

 is about 8 feet wide, and in it a huge bowlder has lodged. The 

 stream rushes down its steep, narrow, winding channel with great 

 force. On the north side there is a huge bowlder just ready to topple 

 off into the channel, which is 50 feet in diameter. On the sides of 

 the channel are several most remarkable rounded cavities worn in 

 like pot-holes, 6 to 10 feet in diameter. One of them occurs 20 feet 

 above the water-level of the creek at the present time. About 100 

 feet above the bridge the stream flows through a narrow gorge not 

 over 4 feet wide, and the water shoots down as in a flume 10 or 15 feet, 

 producing a picturesque effect. In these rocks the jointage is very 

 distinctly defined. The dip of the rock is north about 30°, and the 

 channel has been worn through the rock, so that the north side over- 

 hangs the water, and the water and ice, aided by the jointage, have 

 removed masses like blocks from a quarry. There are two or three sets 

 of master-joints which break the mass into a multiplicity of forms. 

 Sometimes the broken portions are wedge-shaped. The rocks are a 

 coarse, massive granite of a gray color, with large crystals of grayish- 

 white feldspar. The worn rocks, or roches moutonnes, are most admira- 

 bly shown everywhere, and portions crop out in the bottom of the val- 

 ley to indicate the force as well at the extent of the erosion. It is quite 

 possible that if all the debris could be stripped off" the gorge and valley, 

 the grooved or scratched surfaces would be apparent. On both sides 

 of the gorge the worn rocks are seen to the height of 1,000 to 1,500 feet 

 above the bed of the stream. One immense mountain mass on the north 

 side seems to have resisted the eroding forces, so that from base to 

 summit, a height of 1,000 feet, it is smooth like enamel. The vast gla- 

 cier which must have filled up the channel must have been obstructed 

 in its slow downward movement by this projecting point of the mountain. 

 In the side near the base are quite deep, rounded cavities, 2 to 4 feet in 

 diameter, produced by the same causes as the pot-holes. About2 miles 

 above the falls there is an extensive dike of trachyte. It occurs in the 

 form of a vein, 6 to 10 feet wide, running about northeast and south- 

 west. There are many other dikes in this gorge, of different sizes, 

 and I suspect some of them would prove to belong to different ages if 

 more closely studied. The great branch-glacier of Lake Greek must 

 have been 1,500 feet or more in thickness. The valley or gorge is 

 nearly uniform in width, about one-fourth of a mile, and the glacier must 

 have plowed its way along, paring off a great thickness of the gneissic 

 rocks on either side and on the bottom, the low, rounded remnants of 

 which can be seen cropping everywhere from the detritus. The sides 

 of the gorge for 1,000 to 1,500 feet are worn smoothly, and in some 

 places immense blocks of granite have been wrenched from their places 

 and carried down the channel, so that the sides look like a quarry. 

 The most striking feature is the very smooth surface of the sides of the 

 gorge to so great a height, like glass. About six miles above Twin 

 Lakes, in a straight line. Lake Creek forks, one branch extending up 

 northwest, and the other southwest. Both separate again soon into a 

 number of smaller branches, which end in amphitheaters near the crest. 

 About four miles up the North Fork a remnant of the gneissic rocks, 

 left in the wearing out of the valley, has a dip of 50° NW., with a strike 

 southwest and northeast. There are a number of these low ridges 

 rising up in various portions of the valley, showing most clearly that the 

 entire gorge has been carved out of the mountain mass. The dip of the 

 beds would indicate a fracture for the water and ice to commence their 



