42 GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 



the sides of the mountains were covered with little streams of water 

 fed by the melting of the snow, and the great loose masses of super- 

 ficial earth and fragments of rock moved slowly down the slope like a 

 glacier. 



One of the peculiar geological features in this range is the trachytic 

 beds, which appear to be interstratified with the older sedimentary 

 rocks. These igneous layers vary much in thickness, and appear or dis- 

 appear, reach a thickness of 1,000 feet or more, and diminish in a short 

 distance to a few feet, or disappear entirely. And yet, upon the out- 

 cropping face of the great uplifted ridges, or in the deep gulches where 

 not unfrequently 2,000 vertical feet of rocks are shown in their order of 

 superposition, these trachytes seem to have flowed out over the surface 

 of the Silurian quartzites, or, in other words, are interstratified among 

 the old Silurian limestones and quartzites, as if they might be of the 

 same age and have been elevated with them. It is probable that they 

 are not older than the Tertiary period. 



On the summit of the pass or divide between Mosquito Gulch and 

 Evans Gulch, where the great vertical walls which face the Arkansas 

 are so well shown, we have several hundred feet of the quartzites in- 

 clining at a small angle, and resting directly on a great thickness, 800 

 feet at least, of unstratified trachytes. At the base, resting on the schists, 

 are quartzites with micaceous sandstone ; pudding-stones, made up of 

 rounded pebbles of quartz, passing up gradually into a yellow arenaceous 

 limestone, then into a blue limestone rather cherty, then up into a brown 

 quartzite upon which the trachytes rest. This peculiar structure in- 

 cludes all the prominent peaks of this range, extending in a nearly north 

 and south line from Bufi'alo Peak, south, to Quandary, north, and I know 

 not how much farther. There are so many points dependent on the com- 

 pletion of the topographical maps, and the detailed reports of the assist- 

 ant geologists, that these preliminary reports must necessarily be very 

 imperfect. The summing up of these detailed and preliminary reports, 

 which must constitute our final labor, will unite the whole work, the 

 same as the great preliminary triangulations link together into one' 

 whole the detached topograjphical districts, on the final map. 



An examination of the map will show the water-divide between the 

 source of the South Platte and its branches and the Arkansas. Each 

 one of tbese little streams cuts a deep gorge from the crest down 1,000 

 to 2,000 feet, with more or less vertical walls on either side. Nearly all 

 of these gulches, or gorges, have been worked for gold, and the moun- 

 tains prospected for silver; thus the miners have given them local names 

 the origin of which is in most cases obscure. The superficial deposits 

 have been in many cases almost entirely worked, over by the enterpris- 

 ing miner for gold. Placer-mining all over this region has yielded 

 great and brilliant results, but of course they can never be of a per- 

 manent character. All along the west side of the Park range, from 

 Quandary Peak to Buffalo Peak, we pass from one gulch to another in 

 quick succession ; each one of which has employed the enterprising 

 miner to a greater or less extent in search of gold. Not less so the east 

 side ; but we will follow our line of travel, examine the west side for a 

 time, and then return to the east slope again. 



One of the njost noted of the mining gulches in Colorado is the Cali- 

 fornia Gulch. About four millions of gold have been taken out of the 

 placers. There are a few parallel lodes that run about 10° west of south 

 and east of north. Three of the lodes would average about 10 inches 

 between walls. The Five-twenty lode has been worked to the depth of 

 125 feet and 200 feet in length. The Pilot is a " chimney" lode, and is 



