22 GEOLOGICAL SURVEY OF THE TERRITORIES. 



the soiUli side of the same stream, the distance across the synclinal 

 valley is about three miles. As we pass up the axis of this triangnlar 

 anticlinal we find within it an open triangle; or, in other words, high 

 ridges of sandstone incline east, west, and south from the nucleus of 

 mica schists. The sandstones forming the ridges of this inner triangle 

 are much more compact in texture, varying from a sandstone to quartz- 

 ite and pudding-stone. The pebbly portions are scattered irregularly 

 through the mass, showing everywhere that the sediments were depos- 

 ited in shallow and disturbed waters. Indeed, it is seldom that the 

 red groups give any evidence of long periods of quiet deposition. 



Passing over the ridges of sandstone, which rise above the anticlinal 

 valley about 200 feet, we ascend a ridge of black mica-schist, which, on 

 account of its peculiar texture, I have called "bird's-eye schist." The 

 surface of these slate-like shales is covered with circular pits, while the 

 mass of the rock has a wavy texture, the whole reminding one at once 

 of a kind of timber common in our Northern States, known as " bird's- 

 eye maple." The south end of the schist-ridge rises 1,100 feet above 

 the valley of the Big Thompson, at the old stage-road. The second ridge, 

 still farther north, is 1,450 feet, while the highest part of the spur is 

 over 2,000 feet. The highest point is not over 8,000 feet above sea- 

 level. It will be seen at a glance that this ridge or tangential spur, as 

 it might be called, is a remarkable feature in Eocky Mountain struc- 

 ture ; that the internal forces should strike off at a tangent, as it were, 

 elevate a branch ridge from the main chain, and so suddenly, and 

 in many cases abruptly, die out in the plain, is difficult to compre- 

 hend. We shall endeavor to present the facts from time to time with 

 as much detail as possible, leaving the primary causes to become more 

 clearly known as we can accumulate illustrations. The synclinal on 

 the southwest side of the spur continues up until the spur joins on to the 

 main nucleus of granite. The ridges forming the east side of the anti- 

 clinal extend continuously along the east base of the mountains to Cache 

 a la Poudre, while the west side is cut off by the schist-ridge. The 

 synclinal is closed up in a sort of pocket or cmZ de sac, forming the drainage 

 of the ]S"orth Fork or Eed Stone Creek. The red beds lie close up against 

 the granites, while the branches of the Little Fork have cut their way 

 through the ridges, as shown in the small chart. The schists in the 

 spur extend down as a sort of tongue between the uplifted ridges of 

 sedimentary rocks on either side. The schists all incline west or south 

 of west 60° to 80°. The strike of the schist-ridge or spur is about 

 northwest and southeast. The "hogback" ridges on the east side, ex- 

 tending along the base of the mountains to Cache a la Poudre, are quite 

 regular, and incline 20° to 25°. There is usually an interval or valley 

 between the schists and the first ridge, as shown on the surface, though 

 beneath the valley the red sands and sandstones jut up against the up- 

 turned edges of the schists. About five miles to the northward, on the east 

 flank of the mountains, a group of massive red feldspathic granites rise up 

 beneath the schists, and the surface has the appearance of a great morai- 

 nal deposit, so rounded are the detached masses of granite. These worn 

 blocks were scattered over the sedimentary as well as the Metamorphic 

 rocks and show marked signs of former glacial action. Such examples 

 may be found everywhere along the mountain sides. The subject, how- 

 ever, may be more fully discussed in another place. At this point rem- 

 nants of the lower sandstones lie high up on the granites, inclining 60° 

 to 80<^ southwest, while the upper sandstones dip nearly 20° east. The 

 sandstones, as they lie in contact with th« granites, filling up the irreg- 

 ularities of the surface, are composed of a loose aggregate of quartz, 



