188 GEOLOGICAL SURVEY OF THE TEREITORIES. 



tioDS of the rugged group, that has therefrom received its name. Local 

 variations occur quite frequently, but cannot be considered as the rule. 

 Extremely varied and complicated we find the stratigraphical relations 

 of these quartzites. The only fact that could be observed with any ac- 

 curacy, and the only one that is of any direct value, is, that the anticli- 

 nal axis running through the sedimentaries farther westward, continues 

 east through the quartzites, giving rise to the formation of some of the 

 highest peaks in the group. In treating of this axis subsequently, this 

 continuation will also be discussed, and the mention of it here shall suf- 

 fice for the present. Eastward nearly as far as station 21, the quartzites 

 retain their character as such, not changing into granite until near sta- 

 tion 22. To the southwest of station 21 the quartzites dip regularly in 

 a northerly direction, at an angle of about 16°, and are overlaid by 

 trachyte No. 4, horizontally stratified, showing conclusively that cer- 

 tainly the later trachytic flows had nothing to do with the metamorpho- 

 sis, or, at least directly, with the upheaval of the group. At some 

 other points, which shall be mentioned hereafter, evidence was obtained 

 that will exclude the trachytic eruptions entirely from causing any of 

 the changes there observed. 



Along this edge the quartzite is generally of a light grey or white 

 color, containing interstrata of grey, fine-grained schists with twins and 

 single crystals of staurolite. Mount Oso (station 23), reaching an eleva- 

 tion of 13,640 feet above sea-level, is within the quartzitic area, but some 

 distance south of it schists again set in. Mr. WUsou noticed on that peak 

 a fine- grained, white sandstone, in all probability the one that furnished 

 the material for the formation of this quartzite. West and southwest 

 of station 17, the same rock continues, liable to the same lithological 

 changes as at other points. Station 38 is located on it, from where it ex- 

 tends southward for about eight miles more, when granite makes its ap- 

 pearance. The canons cut into this quartzite are extremely precipitous 

 and rough to pass through. Well-defined strata of the hard material form 

 at their edges numerous ledges, which decomposing agents have in vain 

 endeavored to level. Slides, partly snow-slides, partly rock-slides, have 

 often polished the faces of the mountains, or sides of canons, so as to pre- 

 clude all possibility of ready ascent. Glacial action has also had its effect 

 upon the walls, and is made more evident from the distribulion of er- 

 ratic bowlders. Of this we shall speak below. Owing to the compact 

 structure of the strata, and the impenetrable character of the materiar 

 composing them, but little of the precipitated moisture finds its way to 

 any considerable depth. In consequence of this peculiarity, the creeks 

 and streams, if even only flowing a few miles, are very swift and carry a 

 large amount of water. Wherever the drainage has no rapid fall, so 

 that the waters cannot flow off", it stagnates, and forms disagreeable 

 swamps. Owing to the hardness of the rock, and the fact that it so 

 well resists decomposition and disintegration, the debris slopes appear 

 to be constantly balanced, and upon being disturbed, the disturber will 

 not infrequently be greeted by an avalanche of the rocks descending to- 

 ward him. 



A number of large streams head in the Quartzite Mountains, and 

 receive there a bountiful supply of water. Some of the largest are the 

 Kio Florida, Rio Pinos, and Eio Vallecito, all of them tributaries of the 

 Animas, and flowing in a southerly direction. One of the well-known 

 local features that is produced by the steep character of the Quartzites 

 is the Animas Caiion, several miles below Baker's Park. This caijon has 

 very steep sides, and is generally considered impassable. At many 

 points the transition of quartzite into mica schist or the reverse could be 

 observed, but a lack of time did not permit us to follow this out in detail. 



