50 



GUIDEBOOK OF THE WESTERN UNITED STATES. 



South Cheyenne Canyon and the form of the mountains in this 

 part of the State indicate to the geologist, as already explained, that 

 at a time long, long ago this part of the earth's crust was much nearer 

 sea le^'el than it is now. The mountains of Colorado were not then the 

 magnificent spectacles they are to-day but were more like the Ap- 

 palachians. Pikes Peak of that time was probably not more than 

 6,000 or 6,000 feet above sea level, and the plains reached back many 



the other parts of the contact the 

 walls are also steep. The general con- 

 clusion reached is that a tremendous 

 volcanic explosion blew a great hole 

 in the older rocks of the plateau. This 

 hole was subsequently filled, perhaps 

 partly with the fragments produced by 

 the first explosion, including bits of 

 granite and schist and pieces of the 

 trees that were growing on the plateau 



groups of closely spaced narrow fis- 

 sures (sheeted zones) and are partly 

 distributed more or less irregularly 

 through masses of altered granite near 

 fissures. Neither form of dejwsit is 

 conspicuous at the surface, and only 

 experienced prospectors would have 

 found them. The gold is present 

 chiefly in the pale brass-yellow min- 

 eral calaverite, a combination of gold 



Feet 



12.000 

 11,000 ■ 

 10,000 

 9,000 



1 anic co^e.--"--^ 



PossLble.q(itJ:ii-°^— -— ""Bull chff---. 



'-'" ,\!'i ''-~/,'/V( w -''i>"''A'"§"JJ-.^'< 



^. 



B 



Vertical and horizontal scale 



Figure 12. — Sections showing supposed outline of the Cripple Creek volcano. 



at that time. To these materials were 

 added, probably by later eruptions and 

 explosions, fragments of phonolite and 

 related igneous rocks. Finally, as 

 shown in figure 12, a volcanic cone, 

 consisting chiefly of fragments of rock 

 was built up above the breccia-filled 

 abyss. 



After the eruptions had ceased the 

 rocks adjusted themselves to the new 

 conditions. Cracks were formed in 

 them and in these cracks the gold ores 

 were deposited by hot solutions that 

 rose from deep volcanic sources. Rain 

 and streams gradually wore away the 

 cone and exposed the veins thus 

 formed, which the keen eyes of pros- 

 pectors afterward detected. 



The gold ores of Cripple Creek oc- 

 cur partly as narrow veins or as 



and tellurium, associated with quartz 

 and purple fiuorite. Native gold is 

 rare, except in the upper oxidized 

 parts of the veins. The ores average 

 from 1 to 2 ounces of gold ($20 to .$40) 

 a ton, but the gold content varies 

 widely, and comparatively small bodies 

 of very much richer ore have been 

 mined. 



In this district, as in most others, 

 the ore is not uniformly distributed 

 along the veins but is limited to what 

 are known as shoots and occurs par- 

 ticularly where veins cross one an- 

 other. Some of these shoots, such as 

 the one found in the Cresson mine a 

 few years ago, have been extraor- 

 dinarily rich, but the larger mines, 

 like the well-known Portland, depend 

 mainly upon large shoots of ore of 



