EXDLICH.] 



GEOLOGY CONCLUSIONS. 351 



A few words may also be said regarding the distribution of the geo- 

 logical formations over the entire district. 



Granite forms all the higher i^ortions of the eastern edge of the Front 

 range ; but on the northern side of the Arkansas it is covered largely by 

 trachorheites, and, to some extent, by sedimentary formations. Con- 

 tinuing its course westward, it forms the main mass of mountains in the 

 north, whereas the entire southwestern portion is volcanic. The sediment- 

 ary beds of Silurian and Carboniferous age traverse the central portion 

 of the districts in a narrow band in a southeasterly direction, the 

 former edging the latter in the northern i)ortion, disappearing in the 

 south. Again, they reach into the northwest corner of the district 

 coming from the north, and covering about one hundred and fifty 

 square miles. Mesozoic and Tertiary beds are found only along the 

 eastern edge of the Front range, with the exception of one or two 

 isolated patches of small extent. The Cretaceous occurs all along that 

 same edge, extending into the mountains in a few bays of ten to twelve 

 miles in length, and is found in the western portion of the district, a 

 continuation of the formation farther north. 



Volcanic rocks cover the granite partially in the eastern and northern 

 half of the district, forming the high plateaus, while the granite appears 

 in the eroded canons. A few isolated patches are scattered throughout 

 the granites, one of them extending in a very narrow line i)arallel to 

 the Sangre cle Christo range. The largest portion is that forming the 

 southwestern corner of the district, which probably extends consider- 

 ably beyond it both west and south. 



Drift covers San Luis Valley, the upper valley of the Arkansas, and 

 Wet Mountain Valley, besides small portions on the Tomichi, at Union 

 Park, and on Taylor Eiver Valley. 



The mineral resources of this district are confined to gold, silver, 

 iron, coal, and marble, of which mention has been made in speaking of 

 the several sections in which thev occur. 



