MAEVKE.] GEOLOGY STRATIGRAPHY OF THE EAST SLOPE. 153 



Creeks, and just back of the "bog-backs," the straight-banded gneissic 

 and siliceous schists and the irregular red and white garnetiferous schists 

 seem folded into a pretty clear case of a southward dipping anticlinal 

 with the west side thrown over past the vertical. Such a structure, 

 however, would be inconsistent with the general structure immediately 

 west, unless we assume the west side of the fold to be in the normal 

 position and the eastern rocks tipped past the vertical. As some of 

 them lie quite flat it hardly seems as if the inversion could have been so 

 great. Notwithstanding the many observations here made the structure 

 does not seem to have been clearly made out, and no attempt is made to 

 indicate it by the dotted approximate horizon lines. The western slopes 

 of the main range, as well as the other areas of archsean rocks gener- 

 ally, were not studied even as carefully as the east slope, and but little 

 can be said of them. The western slope of the main range, in its north- 

 ern portion whenever it was observed, appeared to have a general west- 

 ern dip, which was also indicated in all the general views obtained of 

 it. Crossing the great trough-like valley of the Upper Grand Eiver, 

 the high southern portion of the Medicine Bow range, where visited, was 

 of a very sharp anticlinal character, the rocks appearing folded quite 

 flatly upon themselves. It is quite possible that the fold is recent and 

 that the sedimentary once mantled over it, lllled the trough of the 

 Grand, and ran far up on the main range. When the broad rolling 

 ridge of the Park range was touched, at the extreme northwest corner 

 of the Middle Park, it presented only a massive granite of tha very 

 coarsest description, with great crystals of feldspar, and no observed 

 structure whatever. 



Many miles south, where the range rises on the great Blue Eiver 

 group of mountains, schists and gneisses predominate. These all seemed 

 to have a pretty uniform trend, following pretty closely the remarkably 

 sharp spurs running out northeastward from the main ridge and dipping 

 southeastward. In Ute Peak the trend runs nearly east and west with 

 a nearly vertical dip. In Mount Byers, the northwest spur from the 

 Berthoud Pass groui) of mountains, the strike was mostly with the spur. 

 The great east-west ridge connecting the Evans group with the Park 

 range, and forming the divide between the Middle and South Parks, 

 was not examined. 



It is unfortunate that more definite and positive results could not 

 have been arrived at, but when the extent of the area traversed, and the 

 short time employed, together with the fact that other rocks demanded 

 attention, and the peculiar difficulties in the way of this special study, 

 are all taken into consideration, the outcome of the season's work can- 

 not be regarded as so very small. The fact that the great front range 

 is practically composed, throughout this region at least, of metamorphic 

 rocks, and that these rocks possess a definite and accessible structure, 

 is certainly shown, and while errors may be found in minor points, yet 

 it is believed that the more general structure of the range as shown in 

 tke map will be ultimately found to be substantially correct. Some of 

 the topographical features of these rocks are dwelt upon in the early 

 part of the following chapter, when speaking' of the upper valley of 

 Grand Eiver, and later when describing the Blue Eiver Mountains. It 

 is hoped that a more complete digest of the notes, with study of the 

 specimens, aided perhaps by chemistry and the microscope, may not 

 only add interesting results to the lithological and metamorphic ques- 

 tions involved, but assistin perfecting the knowledge of the stratigraphi- 

 cal structure of the range as presented above. 



