128 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



the Buckskin glacier, and probably once reached down to the Platte, the 

 actual bottom of the present canon being from one hundred to two hundred 

 feet lower than corresponding portions of Buckskin gulch. Both Mosquito 

 and Buckskin gulches open out into alluvial bottoms below the catton 

 mouth, but the stream in the latter soon runs into a narrow, winding gor-e, 

 which extends for a mile above Alma. The connection of the Buckskin 

 glacier with the Platte glacier, if it ever existed, must, therefore, have been 

 above the low ridge through which this gorge is cut. 



Buckskin section. The most complete and instructive sections of the lower 

 Paleozoic beds and their included sheets of eruptive rock are obtained on 

 the walls of the cafions near their mouths, just before the beds dip down 

 more steeply to the east and disappear beneath the softer slopes of the 

 lower rounded hills or are covered by the alluvial deposits of the streams. 

 That on the south .side of Buckskin gulch, just about the deserted town of 

 Buckskin Joe, is represented by the diagrammatic sketch given in Plate XIII. 

 The total height of the cliff above the valley bottom is here about one thou- 

 sand feet. 



The Archean exposures (a), occupying the lower portion, are largely 

 concealed by huge talus slopes of debris, which in some places extend up 

 so high as to cover the base of the Cambrian, while the Blue Limestone at 

 the top of the cliff is covered by soil. The portion represented in the 

 sketch shows, therefore, only the Cambrian and Silurian beds and the 

 manner of distribution of the intrusive sheets of porphyry and porphyrite. 

 These are here very irregular as compared with sections elsewhere, which 

 is doubtless due to the fact that they are near the northern limit of the bodies, 

 and hence that the intrusive power which forced them between the beds was 

 already diminishing in energy. The upper bed is about fifteen to twenty ' 

 feet in thickness and consists of dark-green hornblende-porphyrite, of the 

 typical variety already described from Mosquito gulch. As shown in the 

 plate, it varies in thickness and often wedges out, its continuation occurring 

 farther on at a slightly higher or lower horizon. At its contact with the 

 bounding sedimentary rocks it becomes more compact, but the sedimentary 

 beds show no caustic phenomena, though they are sometimes slightly con- 

 torted. About thirty feet below this is a second intrusive sheet, also 



