334 GEOLOGICAL SUEVEY OF THE TEREITORIES. 



feldspar, galenite, sphalerite, cerussite, argentite, stephanite, malacliite, 

 and azurite ; the latter two the result of decomposition of fahlerz. The 

 elevation of Eosita is 8,827 feet. 



Descending Hardscrabble Creek, several mines were found located 

 near the upper end of Hardscrabble Caiion. In speaking of the granite 

 of that region, it was stated that a number of variations took place, 

 caused by local accumulation of one or the other mineral constituent. 

 Parallel to these accumulations, sometimes of hornblende, appearing in 

 the form of dik^s, more freqneutlj' of mica, sulphuret-ores have segre- 

 gated, and are being worked to some extent. The strike of the lodes is 

 parallel to that of the gneissoid strata ; the dip also conformable. The 

 Silver Hills mines are of that character, furnishing quite a considerable 

 quantity of fine-grained galena, with argentite and cerussite. Another 

 of similar character, but less ore, is the Barton, mine. Of these mines 

 but little can be said, as they are not deep enough yet (35 feet) to war- 

 rant any definite assertion, but it seems probable that tliey will not hold 

 out very long. 



Resume of section h. — We find along the eastern line of the Front 

 range the same phenomenon of a gradual rise that characterizes the cor- 

 responding portion of the preceding section, only having gone on to a 

 greater extent in the southern part. Here we have, analogous to the 

 occurrence near Pike's Peak, the Carboniferous strata, although at one 

 locality only appearing ujion the surface, indicating a greater activity 

 of the rising, or a more thorough erosion. It is of importance to know 

 that these older formations underlie the beds referred to the Mesozoic 

 period. One of the most interesting and instructive portions of tlie sec- 

 tion is the Sangre de Christo range. A series of sandstone-strata of 

 more than a mile in thickness have been lifted up in one continuous, 

 almost straight, line of forty miles in length ; and while the strain has 

 been too great for most of the strata, while they have broken, and 

 allowed the granite to be forced out to higher relative altitude than 

 they reach, at a single i:*oint this strain has been resisted and the sand- 

 stone-arch remains entire. Comparative regalarity in the arrangement 

 of strata in their tilted position shows that but few, if any, disturbances 

 took place in, or had any effect upon, the immediate vicinity of the 

 Arkansas sandstone. It seems probable that this latter extends across 

 the San Lnis Vallej', perhaps over its entire width, j^erhaps only ]3artly. 

 As trachorheites reach over eastward to the very base of the gravel- 

 bluffs, and neither granite nor any sedimentary beds make their appear- 

 ance to form a transition, it is quite possible that the sandstone may 

 extend a short distance up into the higher lands. Its stretch across the 

 southern part of Wet Mountain Valley seems to me pretty certain, 

 although it could not be determined definitely from a distance. The 

 trachyte has taken in section h a course almost parallel with that of 

 the granite forming the heart of the Sangre de Christo range, and 

 instead of appearing, as in section «, as the result of massive eruptions, 

 it seems in this instance to have been volcanic, accompanied by flows 

 of considerable extent. Besides this difference, there is little resemblance 

 in the general character of these trachorheites to those of the northern 

 section; they are, as a rule, more compact, with less tendency to segre- 

 gate ci-ystallized minerals. San Luis Valley, that probably in late 

 geological times contained a lake of very considerable extent, seems to 

 owe its formation to the gentle slope of the underlying sandstone. 

 Sangre de Christo seems to have contributed a large amount of the drift- 

 material of which the bottom of this valley is made, also the country to 

 the northwest of Poncho Pass. 



