324 GEOLOGICAL SURVEY OF THE TEEEITOEIES. 



place between stations 19 and 20, where the sedimentary rock making 

 up the greater part of the range forms a bridge. Almost throughout, 

 with the exception of the eruptive, the granite preserves a very uniform 

 character, very similar, if not identical, with that of section a, a 

 type that I am inclined to regard as the oldest of that portion of the 

 Eocky Mountains. There is but little variation in the granite of section 

 b, with the exception of local accumulations of mica, whereby a more or 

 less stratified appearance is obtained, and of numerous dikes — partly 

 schistose, with mica, partly hornbleudic — that have some influence upon 

 the character of the surrounding rock. In the Sangre de Ohristo range 

 the eruptive granite is very similar throughout, but totally distinct and 

 different from any other granite found in the section. 



Beginning in the northwest corner of section &, we find the granite 

 identical with that north of the Arkansas, gradually changing, however, 

 in texture toward the south, where it becomes a little finer in grain, has, 

 perhaps, more mica, and therefore alters its structure somewhat. Where 

 Hardscrabble Creek flows out into the more open country immediately 

 east of the granite, the latter assumes nearly the character of gneiss, 

 becoming more lamellar, and showing a decided tendency to stratifica- 

 tion. The color of the feldspar, too, usually is a little lighter than far- 

 ther north, and the mica black. In its main outlines, however — in the 

 weathering .and formation of canons-^there is but little difference. On 

 station 13, near Oak Creek, a very curious phenomenon was noticed. 

 Naked rocks compose the crest of a narrow ridge running approximately 

 east and west, upon which the station was located. On the north side 

 the rock was perfectly planed, about 100 feet in length and 50 feet high. 

 This planed surface was striated horizontally with strise varying from 

 1 to 4 inches in width. Toward the west they bend off from the hori- 

 zontal direction, falling downward. A good idea of it can be obtained 

 from the illustration. At first a vision of glacial action presented itself; 

 but upon examination it was found that the large slab reclining against 

 the base of this rock was striated on its under surface in precisely the 

 same way. It is evident, therefore, that this striation must have been 

 produced by a friction of these two portions of rock upon each other, 

 and that the motion must have been first a horizontal, then a declining 

 one. As to the cause producing this phenomenon, I am unable to give 

 any positive statement. I merely wish to remark that glacial action 

 must be out of the question entirely, being precluded by the orographi- 

 cal character of the surrounding country. 



Toward the northwest of the great wedge-shaped mass of granite, it 

 becomes very coarse-grained, is of dark color,' and frequently shows 

 apparent stratification. Having observed the structure of granitic 

 masses throughout the country surveyed during the last season, I have 

 thought to observe that wherever the feldspar is very predominant in the 

 granite, particularly as regards its occurring in continuous pieces, the 

 granite presents a more or less stratified appearance, owing to the influ- 

 ence of the planes of cleavage. Upon weathering, this becomes more 

 apparent'still. 



An entire change is noticed, however, in the character of the granite 

 as soon as the Sangre de Christo range is reached. Almost throughout 

 the entire length of this range, the core of it, the tops of the higher 

 peaks are formed by this new variety. It occurs as a central mass of the 

 range, anatomically speaking as its backbone, and is only bridged over 

 at one single point as far as could be determined. On either side of it 

 lay the heavy strata of Arkansas sandstone, dipping off from the gran- 

 ite at steep angles. At first sight this rock might be mistaken for 



