HAYDEN.j 



GEOLOGY SOUTH PAEK. 37' 



is such tliat the basset edges projsct from the south side, while on the 

 north side the slope is quite moderate. The caiion is partly oue of 

 fracture as well as erosion. The stream has not cut the strata quite at 

 right angles, but slightly across the dip. The principal rock is a very 

 hard, black gneiss or schist, with seams of yellow feldspar, varying from 

 a few inches to several feet in thickness, running across the strata at 

 different angles. Some of the seams contain quite large masses of 

 quartz, but feldspar predominates. Sometimes the quartz is interstraji- 

 fied with the schists for a short distance, running out, however, at both 

 ends. In cutting the road along the north side of the Turkey Creek 

 Caiion an old dike is exposed, with feldspathic quartzite on one side and 

 a seam of feldspar on the other. The dike-matter is filled with masses, 

 of greater or less size^ of the adjacent schists. • This dike would never 

 have been exposed but for the wearing out of the gorge by water and 

 ice. Igneous rocks of different ages are thus exposed at various locali- 

 ties all through this front range ; .seams of quartz or feldspar are so 

 numerous, intersecting the schists in every direction, that it would re- 

 quire a most detailed study to describe them properly. Pockets of 

 mica occur frequently in these seams. About a mile up the caiion are 

 two dikes of syenite 10 to 15 feet wide, rising up in the form of a wedge, 

 but separated by about 8 feet of feldspathic granite. The schists here 

 present to the eye the appearance of utter chaos. The study of the 

 details would reveal a warping of the bedding that would be quite 

 remarkable. Layers several feet thick are warped, or dished, at least 

 half the circumference of a circle. The aggregate inclination seems to 

 be 20° east of south. The lower thin layers of schist are in some places 

 crushed in a remarkable degree, while higher up toward the summits 

 are thick massive beds of feldspathic granite in a horizontal position. 

 For about five miles up the canon the scenery is very rugged on both 

 sides, the valley widens out somewhat, and the mountains on either side 

 soften down and are covered more or less with debris and thin soil, on 

 which grow grass and pine trees. Near the junction and for some miles 

 beyond the rocks are massive granites, of which the great mountain- 

 peaks in the vicinity are composed. The surface is covered with groups 

 of weather-worn granitic masses resembling old ruins. The peculiar 

 forms of these masses determine to a great extent their texture. The 

 coarse feldspathic granites disintegrate easily, and peel off in thin, cir- 

 cular layers, giving to them a smooth, rounded appearance, while the 

 finer-grained, more compact granites are still angular. The varieties in 

 texture^give form co the surface-scenery over a very large area, and no- 

 where is this fact better illustrated than in these mountain-districts. 

 The great orographic lines were undoubtedly determined by upheaval, 

 but the x)resent surface-forms were due largely to erosion. We shall 

 endeavor to show, from time to time, that sufficient importance has 

 never been attached to this agent in molding the lineaments of the 

 earth's surface ; that although the proofs of upheaval are everywhere 

 apparent, and in many localities most probably those of depression, yet 

 the immediate forms of the surface thus produced have almost entirely 

 disappeared under the effects of erosion or weathering. Many of the 

 water-courses have probably followed lines of fracture, so that the two 

 agents, upheaval and erosion, may have united to produce many of the 

 mountain-valleys. There is one interesting feature in connection with the 

 mountainous districts of Colorado, which is now apparent in the valleys 

 of the Colorado or front range. These grassy areas are fast being 

 occupied by a mountain-population, sparse, it is true, but a very thrifty 

 one. The grass not only covers the valleys in the elevated regions, but 



