328 GEOLOGICAL SURVEY OF THE TERRITORIES. 



sandstone it crops out again, leaning up again at Granite, on the west 

 side of the valley, with a dip to the east. It is very probable, therefore, 

 that the Carboniferous strata extend across that northern end of the 

 San Luis Valley. This western outcrop is small, about five or six miles 

 in length, but very narrow, dipping gently under the diluvial deposits. 

 East of Mosco Pass the sandstone seems to extend across the lower por- 

 tion of Wet Mountain Valley, as it was found a little west of stations 

 83 and 84, on the western slope of the mountains, and the aspect of the 

 valley at that place indicates a crossing of the sandstone. Limestone 

 accompanies the sandstone at several places in a long patch west of 

 station 19, dipping conformably with it, with the exception of one small 

 local fold ; but besides this occurrence there are several beds of limestone, 

 interstratifled with the sandstone, one of which afforded a few fossils. 

 On the western side of Roman's Park, where the sandstone crops out 

 again, limestone is also found with it, analogous to the limestone of 

 section «, overlying the Arkansas sandstone. In connection with this 

 formation I have to mention a very peculiar conglomerate, found only 

 once at a high elevation. The Christoues, upon the highest of which 

 station 17 was located, are entirely composed of a conglomerate, con- 

 taining fragments of granite, gneiss, hornblende-rock, mica-schist, pink 

 porphyry, garnet-rock, epidote-rock, and quartzite. These fragments are 

 not rounded by action of water or atmospheric influences, but have 

 perfectly sharp, angular outlines, and are cemented by a hard, gray 

 quartzitic paste. Their size ranges from half an inch to several feet in 

 diameter. In weathering they resist longer than the matrix does, thus 

 studding the almost perpendicular walls of the mountain similar to the 

 ornamentation of Gothic spires. A little south of station 17 a dike. of 

 pink porphyry has broken through the conglomerate, and makes its 

 appearance near the top of a peak. Stratification can be noticed to 

 some extent in the arrangement of the conglomerate, and the strata dip 

 off very steeply to either side from the crest of the range. Besides these 

 more connected masses of Carboniferous rocks, an isolated i^oiut of ex- 

 posure was found near Boggs's ranch, in the southeast corner of section b, 

 where the rise of the main granitic body seems to have been sufficient 

 to bring out this formation besides the Mesozoic beds. It is of but small 

 extent, identified by fossils found in the grayish limestones and shales. 

 As in section a, the Carboniferous here, too, is succeeded by the Mesozoic 

 formation. 



On Plate XIII, section c, an ideal section through the Sangre de 

 Christo range is given, showing at once all the various occurrences 

 throughout the entire range, and its general character. Eestiug imme- 

 diately upon the granite are the Arkansas sandstones on either side, inter- 

 stratified with limestones, (e,) and shales, {d.) Dikes of hornblende-rock, 

 (/,)with a strikeofnorth to south, traverse the sandstones. Toward both 

 east and west the dip gradually decreases. As in section a, the Trias- 

 sic and Jurassic beds occur along the eastern edge of the granitic Front 

 range. Directly south of the Arkansas they begin, occurring in isolated 

 patches all the way southward until Hardscrabble Canon is reached. 

 From this point they cover more ground, until a short distance below 

 Bogg's Eauch, where they entirely cease. Stattou 78, southeast of 

 Hardscrabble Creek, is located upon such a sandstone, of dark-red color, 

 lithologically identical with that farther north. The dip throughout is 

 to the east and a little north of east, steeper at the base of the mount- 

 ains, more gentle nearer to the plains. South and southeast of station 

 78 they iijcrease considerably in thickness, forming bluffs of nearly 1,000 

 feet in height. Deep gorges, at times narrow, sometimes wider, in the lat- 



