HAYDEX.] 



GEOLOGY SOUTH PAEK. 45 



mit, while the stratified quartzite cap only the highest peaks of the 

 Horseshoe and other cones in the vicinity. The quartzites here are 

 very hard, but brittle, breaking into small fragments greatly meta- 

 morphosed, though distinctly stratified, and remind one of the quartzites 

 of the Uintah Mountains. Below the massive quartzites are very hard 

 limestones, out of which considerable quantities of silver-ore are taken. 

 Below the limestones are 50 to 80 feet of a i)eculiar rock, composed 

 largely of yellow jasper. The dip of the strata in the north branch of 

 the Horseshoe is about 21°, and in the Horseshoe itself about 19°, north 

 of east, though it is quite variable. The Horseshoe is a most singular 

 mountain-form. The excavation here has wrought out a circular or 

 semicircular form, which suggested the name of Horseshoe Mountain. 

 On the south side a ridge runs down the gorge-like valley for four miles, 

 with an average dip of 13°, and then a high mountain occurs, in the 

 base of which the gneiss projects up 500 feet, while on the east side and 

 on the summit the lowest quartzites are again seen in contact with the 

 gneiss. The most remarkable faults in the strata occur here. In the 

 carving out of the Horseshoe amphitheater the granitic schists are ex- 

 posed at the bottom, and continue down for a short distance, when they 

 are concealed by the debris. Only the stratified beds are seen in the 

 walls of the gulch on either side. Here and there the schists rise up to 

 considerable heights. The sedimentary beds may rest on the schists 

 lower down in the valley, or on the high peaks 2,000 feet above. The 

 remarkably irregular surface of the underlying schists is hardly due to 

 erosion prior to the deposition of the sedimentary rocks, but to the 

 internal forces that have thrown all the rocks in this region into such a 

 remarkable chaotic condition. We do not find here the intruded beds 

 of trachyte on quite so large a scale as on the west side of the range. 

 The trachyte, however, shows itself about four miles below the depres- 

 sion of the Horseshoe, changing all the rocks to a greater or less extent 

 with which the igneous material comes in contact. 



This gulch has really three heads, of which Horseshoe forms the middle. 

 The evidence of the gradually slow excavation of these amphitheaters 

 is well shown in each. That the wearing out of the depressions may 

 have been more rapid in former times I do not doubt j perhaps, during 

 Glacial or Post-Glacial times. We shall hereafter discuss the subject of 

 the great Glacial peiiod, which must have held sway over all this region. 

 Ice, snow, and water are still important agents, though their action is 

 slow and the results hardly perceptible in a century. It would be ditfi- 

 cult to fix any very definite angle of inclination for the stratified rocks. 

 Sometimes it is nearly horizontal, and again nearly vertical. In the 

 Horseshoe district the dip will vary between 12° and 25° generally. A 

 typical section of the sedimentary rocks in this region may be found in 

 the gulch to the south of the Horseshoe. The strata which rest upon 

 the schists there present a nearly vertical wall for about 800 feet. The 

 schists as they occur in the bed of the stream appear to be vertical, with 

 grayish brown quartzites resting directly on the edges, passing up into 

 a cherty limestone. This is quite variable in texture, though the joint- 

 age and lines of stratification are clear. On the southeast side of the 

 gulch, at the very head, there is a massive wall of quartzites and lime- 

 stones 800 feet high ; then comes a bed of intruded porphyritic trachyte, 

 about 400 to GOO feet thick, and above this comes 300 feet of very hard 

 dark brown quartzite, evidently partially metamorphosed. Then comea 

 an interval, obscure on the surface, but composed of a dark slaty shale, 

 with layers of dark impure limestone. There are alternate beds of 

 limestone, quartzite, sandstone, and shale through what I estimated to 



