CHAPTER I. 



METAMOEPHIC AEEA. 



The nietaniorphic area sets in south of the headwaters of the Eio 

 Grande, at station 17, and from there continues southward for about 

 twenty miles, eastward to its extreme limit for twelve miles. For four 

 miles east of station 17 these rocks follow the course of the river, i. e., 

 more properly speaking, the course of the river is determined by them, 

 and then they bend off southward again, for the same distance, influ- 

 encing the course of a creek opposite Pole Creek. After that, their 

 border runs in a southeasterly direction, inclosing all that high mass of 

 mountains that we have designated as the " Quartzites." On the west- 

 ern side they approximately follow the course of the Eio Animas down 

 to Animas Park, where the sedimentaries set in, occuring likewise also 

 in the valley. As an estimate, it may be said that this continuous area 

 of metamorphics covers three hundred and fifty square miles. A num- 

 ber of smaller patches of the same class of rocks occur at various other 

 points, but are of less importance. The lowest portions of Cunningham 

 Gulch contain a continuation of the area from station 17 ; northwest 

 of the Eio Grande Pyramid (station 21), a coarse-grained granite crops 

 out near a little lake. The canon leading down northward from Han- 

 die's peak (station 14), contains a similar granite ; on Lake Fork 

 Creek, opposite station 12, granite again occurs, forming a few small 

 hills, and it is found also around station 7, extending for some miles 

 along the base of the ridge. In the lowest part of White Earth Canon 

 a schistose rock crops out, that must be referred to this group. It is 

 overlaid by trachytes, and covers but a small area. 



This large metamorphic group, from a geognostic and geological point 

 of view s is one of the most interesting features that the district presented. 

 Lithologically considered, almost every variety belonging to that class 

 can be observed, although the mineralogical variations are not great. 

 Near the northern border and toward the middle, quartzites and schists 

 predominate, while granite appears toward the east and south. Mostly 

 the quartzites are of a white or gray color, gradually becoming filled 

 with mica or chlorite, thus turning into schists. Numerous small veins 

 of white quartz traverse this rock, which must at one, or perhaps vari- 

 ous times, have been subjected to considerable strains, whereby the 

 small fissures were produced. At station 17 the rock assumes very 

 much the character of a gneiss ; the mica is black, quartz gray, feldspar 

 whitish, but only little of it, texture and structure gneissoid. Going 

 but a few miles to the north, this description will hold good no longer. 

 Although for some distance volcanic rocks cover the schists, there is no 

 doubt in my mind that the two — that of station 17 and that of Cunning- 

 ham Gulch — are in connection with each other. The feldspar, however, 

 and the mica have disappeared and are replaced by chlorite. Structur- 

 ally there is no marked difference between them ; it is expressed miuer- 

 alogically only. Again, traveling southward from station 17, we first 

 find a large quantity of a gray micaceous schist, rich in quartz, and soon, 

 near station 25, the mica begins to disappear, so that we have a gray 

 quartzite. This is the predominating rock throughout the highest por- 



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