ENDLICH.] VOLCANICS. 201 



and but little mica. A small quantity of No. 2 is found below this, 

 weathering very readily into small scaly fragments. This rests upon a 

 coarse-grained metamorphic graflite, which crops out at a number of 

 points, and is a continuation of that found at station 22. To the west- 

 ward, about nine miles, the characteristic strata of No. 4 set in, forming a 

 higb, flat country, in striking contrast with the adjoining quartzitic 

 region. This continues upward to the headwaters of the Rio Grande. 

 Oa the north side of the river, a short distance west of Lost Trail Creek, 

 there is an excellent development of No. 1, and Nos. 2 and 3 above it. 

 Very unique bluffs, about 8(30 feet in height, have the appearance of 

 variegated marls more than that of volcanic deposit. Presenting a very 

 marked stratified appearance, it may be observed that this is due mainly 

 to the accumulation of coloring material (oxygen compounds of iron) 

 in certain horizontal zones. Not far up the river is this outcrop con- 

 tinued, however, as it slightly changes its course and the breadth of its 

 valley. As the dip of the flows or strata at that locality is a south- 

 easterly one, the disappearance of the lower stratum becomes a neces- 

 sity, from the position at which they are exposed. Only on Pole Creek, 

 about three miles from the Rio Grande, and near the junction of the 

 two, they crop out again, showing, in the former case, fantastic forms 

 and groups that an enthusiastic admirer might readily construe into 

 figures resembling human shapes. 



Along the north side of the river, the rocks of No. 2 weather in 

 abrupt bluffs, showing horizontal seams, and irregular inclosures of 

 porphyritic pitchstone, that from a distance have the appearance of 

 cavities. Above them are the layers of No. 3, dipping conformably 

 at an angle of 2° to 4°, overlaid in turn by the conglomerate that was 

 mentioned from the Rio Grande Pyramid. About two miles east of 

 Pole Creek is station 18, with an elevation of 13,658 feet, capped by a 

 prominent cap of black basalt. This feature will make the peak dis- 

 tinguishable from any others in the vicinity. Westward of Pole Creek 

 the character changes; we already begin to reach the section which, in 

 the beginning of this chapter, was termed the mountain region. Mount 

 Cauby is the first one that presents the characteristic " red stratum/' 

 We have approached that area which was not flooded by the trachytic 

 eruptions simultaneously with the regions farther east, and although 

 only a few miles distant, we find that this peak, at an altitude of about 

 12,700 feet, shows the lower members of No. 4. Weathering with all 

 the brilliancy that colors originated by ferric oxygen-compounds can 

 produce, it presents, in its variety of shades as well as its elongated 

 pyramidal form, one ot the most striking features of the valley. But 

 a short distance northwest of this mountain are the sources of the Rio 

 Grande, which for more than 90 miles flows through one continuous 

 area of volcanic country. 



In concluding the consideration of the formations bordering this river 

 and its principal drainage, I wish to say a few words regarding the ex- 

 traordinary regularity shown both in the mineralogical development 

 and the distribution of the rocks in question. Below the junction of 

 Pole creek, the most regular development may be said to begin. One 

 i*tratum upon the other is found to be in its normal position, and speci- 

 mens taken miles apart would readily be mistaken for those of the 

 same numbers occurring at other localities. Although deep ravines and 

 narrow gorges frequently traverse the sides of the long ridges, or even 

 cut them, this result seems to be owing to anything but very destruct- 

 ive activity. At some points, certainly along the Rio Grande, the view 

 can hardly be repelled that the canons must have been formed by a sep- 



