326 GEOLOGICAL SURVEY OF THE TERRITORIES. 



small quantity of quartz and still less mica. The color is a dark brown 

 to black. At a few points the mica predominates, changing it into 

 mica-schist. From those high localities the hornblendes come down 

 northward into the foot hills, until near station 4 they disappear again. 

 In speaking of section c we will have occasion to dwell upon these rocks 

 at more length. 



With this the Antizoic rocks of section b are exhausted, and we go on 

 further to the sedimentary. The Silurian is again found, although in 

 small quantities. It skirts the foot-hills bordering upon the Arkansas 

 valley in section c, and a small continuation of this belt has reached sec- 

 tion b. Southeast of station 4 a narrow strip of but a few miles in 

 length appears, dipping oft' toward the north. Of the Carboniferous, 

 however, section b contains more than the two others. That mass of 

 Arkansas sandstone described in section a changes its course slightly 

 to the southeast when crossing the Arkansas, and forms the main bulk 

 of the Sangre de Christo range, where the thickness of its strata is 

 remarkable. The lower limestone that we have farther north also ap- 

 pears immediately south of the Arkansas, near the junction of the South 

 Arkansas, and accompanies it for the distance of about fifteen miles, 

 uniformly dipping oft" from the mountains toward the river. As no fos- 

 sils at all were found in its strata, it was simply determined by its rela- 

 tive position to the Arliansas sandstone and its petrographic features. 

 Anpther little patch of it appears about five miles northeast of station 

 16, where the clip of the strata is inverted. Opposite station 5, the Ar- 

 kansas sandstone forms the bed of the river for several miles, and 

 crosses over on the south side. A How of trachy tic lava, coming from 

 the north, reached this point south of the river after the sandstones had 

 already been disturbed, and showed a considerable dip to the northeast. 

 By means partly of atmospheric, but mainly in consequence of the irri- 

 gation, this ridge of sandstone was cut into several small hills, five or 

 six of them, each one provided with a trachytic cap, growing thinner 

 in proceeding eastward. Two cuts annexed will serve to illus- 

 trate this i:)oint. At the northern end of the Sangre de Christo 

 range, tlie sandstone again appears, and spreads as it continues on 

 southward. At first, north of Hunt's Peak, its dip is nearly north, 

 but soon, upon going south, turns to the northeast. From the 

 apex of the range* downward, the angle of the dip diminishes; but 

 quite a number of local slides and disturbances create exceptions to 

 this rule. All along the range, with the exception of one point, at sta- 

 tion 20, the granite comes up through and separates the sandstone; 

 bat at this place a bridge of very considerable thickness, probably 

 about 800 to 1,000 feet, is formed by the sandstone, extending horizon- 

 tally about two miles. Here the sandstone forms an arch, that is exposed 

 upon almost its entire section, with the granitic bowlders, in the deep 

 caiion immediately aside and in front of it. As these bowlders cannot 

 have been brought there from any point outside, it may be concluded 

 that they are there either in position, or very nearly so. The strata 

 overlying this arch form steep smooth peaks of very considerable alti- 

 tude. Upon the edge of one of these station 20 was located ; on another 

 one was station 19. A section drawn through the arch will give an idea 

 of the relative position of the strata. In the center the eruptive granite 

 (a) shows, while the strata directly above it are obscured by debris. 

 Farther up we reach the bridge, dipping oif on either side, (&,) vfith the 

 strata lying across unbroken. Heavy beds of red sandstone dip off on 

 either side, with steeper jirecipices and slopes on the western than on 

 the eastern side. Interstratified with the sandstones are beds of dark- 



