endlich.] METAMORPHICS. 189 



Could it have been accomplished, probably some very interesting facts 

 might have been elicited. 



Less in horizontal extent, but just as well marked in their structure, 

 are the schists. Scarcely at any point were they found entirely free from 

 bands of a more decidedly quartzitic character, but are generally easily 

 distinguishable by their darker colors. They, too, show very much 

 variation in dip and strike, owing, probably, to small local contortions 

 and slides. A general dip northward on the one side of the anticlinal, 

 and southward on the other, may be observed, however, and to some 

 extent determines the outlines of the mountain-sides, their more or less 

 precipitous character. As a rule they seem to be older than the granite, 

 but it was not possible to establish this point beyond a doubt, as the 

 above-mentioned disturbances have produced so many abnormal posi- 

 tions of the beds with reference to each other that it becomes a matter 

 of great difficulty to establish their true relations. Schists were found 

 at no other localities in the district, except in the Quartzite group, and 

 a few points immediately adjacent. That they extend for some distance 

 under the trachytes, I am very much inclined to believe, but it must 

 be at considerable depth. 



Near station 22, the granitic area sets in, continuing from there 

 southward toward the sedimentary ridges. As a rule, the granite may 

 be said to be coarse grained, with two feldspars. In contradistinction 

 to the quartzites the granites form less steep and rugged points, owing 

 to the facility with which atmospheric agents act upon their mineral 

 constituents. Southward this rock sets in, a short distance below 

 station 23, and from there continues west to the Eio Animas, forming 

 the bed of that river for about nine miles. All the granite in this 

 southerly region shows a remarkably regular stratification, not only an 

 apparent one, produced by the main cleavage-plane of the feldspar or 

 mica lying in one direction. True to what was stated above, the dip of 

 the strata is in conformity with that of the quartzites and schists, away 

 from the anticlinal axis toward the south. Generally it is not very 

 marked, but still reaches 7° to 10°. All along the Animas we did not 

 observe the junction of the sedimentaries with the granite. The latter 

 was exposed in the valley, while the former appeared in steep bluffs on 

 either side. From the dips observed, however, it became evident that 

 the two were conformable, and later in the season we had occasion to 

 verify this fact. Owing to the stratification of this metamorphic rock, 

 and furthermore to its gentle southward dip, it forms rounded bowlders, 

 in positu, that bear a striking resemblance to the roches-moutonnees, but 

 I am not prepared to regard them as such only. 



It may be well to give the mineralogical characteristics of a few of 

 the most frequently observed varieties of this granite before proceeding 

 any further. 



a is a coarse-grained variety, composed of orthoclase, oligoclase, 

 mica, and quartz. The orthoclase is pink, translucent, sometimes in 

 Carlsbad twins, and is the predominating mineral. No parallel arrange- 

 ment of the main cleavage-planes can be observed. Oligoclase is white 

 to light-gray, somewhat inclined to decomposition. Mica is black, very 

 thoroughly mixed in with the other minerals, not crystallized. It is prob- 

 ably biotite, and assumes when decomposing a splendent brown color. 

 Quartz is yellowish to gray with a decidedly greenish tinge. It is least 

 in quantity as a rule. As an accessory mineral, magnetite may be 

 mentioned. This variety is the one most frequently found, and ex- 

 tends, with local changes, certainly from station 22 southward to sta- 

 tion 52, from there west, past station 48, over to the Animas. It weathers 

 readily and forms sands and small irregular bowlders, b. Another variety 



