22 DESCRIPTIVE GEOLOGY. • 



the greater number of observed dips was to the eastward. All the beds 

 near the summit, where observed, seemed inclined at a low angle to the 

 eastward. It may be stated that beds were noted dipping at all angles, 

 from a few degrees above the horizontal up to 70° or 80°. Where these 

 high dips were seen, the strata were usually finely laminated dark schistose 

 rocks. 



No case of decided non-conformity was remarked in the entire series 

 of beds, and their comparatively uniform character would indicate that they 

 belonged only to one division of the Archaean rocks ; while, from their sim- 

 ilarity to other localities, they may be, without much doubt, referred to the 

 Laurentian. 



The rocks of the Colorado Range are almost exclusively made up 

 of a series of crystalline, highly-metamorphosed granites, gneisses, mica- 

 schists, and sparingly of hornblende-schists, of varying lithological habit, 

 but great unifonnity of constituent minerals. The granites are made up 

 chiefly of grayish- white granular quartz, rarely in large masses or crystals, 

 orthoclase-feldspars, both red and white, some triclinic feldspars, but in very 

 subordinate amounts, and particles of black mica, which, although never 

 abundant, is most always present. In their physical characters, the gran- 

 ites vary considerably in color, texture, compactness, and in their tendency 

 to develop more or less of a parallel arrangement of their minerals, and to 

 assume a gneissoid structure. Few localities would seem to offer a better 

 field for the study of the gradual transitions from massive granites to well- 

 defined gneissic schists, thinly laminated, and with a distinct bedding. Fre- 

 quently, these gneissoid bodies will appear as lenticular masses, and as inter- 

 calated beds in the great granitic masses. On the other hand, the gneissic 

 rocks will contain irregular zones and knobs of coarse granite. The rapid 

 transition from the one to the other would appear to be of rare occurrence, 

 except in the case of thin beds of mica-schists and slates in the massive 

 granites. There are many rock masses in which the bedding is very indis- 

 tinct, but which, nevertheless, show, in the quartz, feldspar, and mica, a ten- 

 dency to arrange themselves in parallel bands. 



The region of Long's Peak is a favorable one for the study of both the 

 massive granites and those with a slightly-banded structure, but which must 



