60 



GEOLOGICAL SUEVEY OF THE TERRITORIES. 



that have fallen into the channel, and j)resents a picturesqne view 

 to the traveler struggling along over the narrow trail, high up on 

 the mountain side. But wherever the water forms an eddy, so that 

 it is even moderately quiet, the number of fine, large trout that can be 

 taken out within a limited period would astonish the most experienced 

 fisherman. Above the canon the rocks return at once to their igneous 

 character. This is readily shown by the differeuce in the appearance 

 of the surface features. Although the granitic portion is higher and 

 more massive in its general aspect, yet the surface is rounded and 

 much of it covered with debris that admit the growth of grass, while 

 the volcanic rocks give a jagged ruggedness to the outliue. Outflows of 

 dark-brown basalt, apparently of late date, mingled with huge masses 

 of breccia, can be seen on either side of the valley to the summits of 

 the mountains. The foot-hills on either side are certainly composed 

 of breccia for several miles, which, decomposing, gives to the surface 

 the appearance of the remains of an old furnace. Perhaps it would be 

 better to compare it to a modern volcanic district. The debris has the 

 great variety of colors peculiar to the remains of modern igneous action. 

 The inclosed fragments are mostly angular, or slightly worn, and vary in 

 size from minute i^articles to masses two feet in diameter, though they 

 are mostly small. Some of the rounded hills are quite red on the sum- 

 mits, as if covered with cinders. The nuclei of the mountains are granite, 

 however, although the basis rocks are mostly concealed by the outflows 

 of volcanic material. On the east side, the river cuts close to the base 

 of the mountains, but on the west side, there is quite a broad belt, com- 

 prising the foot-hills, which are composed of basaltic conglomerate, 

 covered thickly with the debris of the same. There is here a small lake, 

 200 yards long and 50 yards wide, occupying a depression among the 

 hills. The margins are covered with piles of volcanic debris^ which give 

 it the appearance of an old crater or fissure. The basaltic rocks rest 

 upon the upturned edges of the metamorphic rocks, the former inclining 

 in all directions, while the latter, on the west side of the river, dip west 

 and northwest at all angles from 10^ to a vertical side, while on the east 

 side they incline east and southeast, at an angle of 60°. For a distance 

 of two or three miles the mountains on the east side are so worn off that 

 they present a vertical face, which reveals the inner character well. Al- 

 ternate beds of a kind of somber indurated clay, volcanic debris, and bas- 

 alt of various colors, continue all the way up for a thickness of several hun- 

 dred feet. These rest npon a reddish feldspathic granite. In some places 

 the melted basalt was x^onred over the surface of the granitic rocks, 

 filling up the irregularities and penetrating the fissures so that it gives 

 the sides of the mountains a mottled appearance. The volcanic and 

 granitic rocks are mingled together in such confusion that it would re- 



Fig. 10. 



quire a long, tedious 

 study to separate them. 

 On the west side of 

 the Yellowstone River, 

 about ten miles above 

 the second canon, there 

 is an exhibition of up- 

 lifted strata. 1 1 is some- 

 times called Cinnabar 

 Mountain, from a 

 brick-red band of clay 

 which extends from 

 the summit down the side, and was supposed to be cinnabar. A portion 



CINNABAR MOUNTAIN. 



