58 GEOLOGICAL SURVEY OF THE TERRITORIES. 



strata 2,500 to 3,000 feet, composed of alternate beds of sandstones and 

 conglomerates with thin layers of clay or shale. These sandstones vary 

 very much in structure in the same layer, from a fine-grained sandstone 

 or quartzite to a rather coarse conglomerate. These chauges may occur 

 in different portions of the same layer or at different positions in the 

 same group of strata. The lower portion of the canon is composed of 

 rather compact sandstones, but toward the summit the rocks become a 

 brick-red and are formed of rather loose sandy material. All the rocks 

 vary in color from a dark dull purple to a brick-red, depending much 

 on the influence of heat. There is a considerable degree of change in 

 these rocks from heat, but only in a few cases amounting to complete 

 metamorphism. These massive walls and pyramids are often inter- 

 sected with dikes which have filled either vertical fissures or not un- 

 frequently have been thrust between strata, forming local beds of 

 rhyolite, sometimes of great thickness. The dividing ridge forms a 

 curious zigzag line, often so narrow as to be almost impassable to one 

 on foot. 



Enormous amphitheaters have been slowly carved put of the dividing 

 ridge at the head of each little branch. Without speculating upon the 

 character of the forces which were at work here in the far past, whether 

 they were far more intense in their action than at present, we may infer 

 that at this time they operate exceedingly slow. Portions of the divid- 

 ing wall are falling all the time, from the influence of frost or water, and 

 in many instances the amphitheaters extending back over the true di- 

 vide, sometimes even breaking through the axial ridge. Usually a vast 

 accumulation of debris may be found damming up the gorge at various 

 distances from the immediate head of the amphitheater, thus giv- 

 ing origin to a small lake, the waters of which gradually soak 

 through the debris, and, coming out on the lower side, gather into a 

 small stream. It seems hardly possible that at the present time there 

 are any agents in existence that could have transported this delris 

 down the gorge. It must have required a considerable quantity of water, 

 with large masses of snow or ice, for the debris is often composed of 

 large masses of rock that could only have been moved by floating ice. 

 In the valley of Roaring Fork, the morainal deposits are remarkable 

 for their thickness. The surface is covered with huge bowlders, some 

 angular and others partially rounded. The terraces are very conspicu- 

 ous, rising, in some instances, to 1,000 feet or more above the bed of the 

 stream and strewed over with huge bowlders. None of the stray ma- 

 terials in any of these valleys or gorges seem to have been transported 

 a very great distance, and never, under any circumstances, is there any 

 drift or glacial deposits from a neighboring drainage ; in other words, 

 the loose material does not pass from one independent valley to another. 

 So it is all over the Rocky Mountain region so far as I have observed. 

 All the drift or Post-pliocene deposits are local. 



I regret' that, for want of time, this meager account of so important 

 a range of mountains must be closed. In the final report, in quarto, 

 which will accompany the atlas of maps, we hope to present a more 

 careful review of each range of mountains, with their relations to each 

 other. 



In this report I have attempted to number the plates in consecutive 

 order, but the sheets of sections and maps could not be so numbered, 

 but will probably be clearly understood. 



