272 GEOLOGY AND MINING INDUSTEY OF LEADYILLE. 



Lake beds below Dome fault and the depth of the contact are derived 

 from actut.l data as far west as the Coon Valley; beyond that they are the- 

 oretical deductions. 



Section i. Section I is a broken line following, as near as may be, the 

 crest of Long and Derry Ridge from West Sheridan Mountain westward. 

 It shows the beds left on the crest of West Sheridan ; the anticlinal struct- 

 ure developed on Long and Derry Hill, between Mosquito and Weston 

 faults; the uplifted block of ground between Weston and Union faults; 

 the outcrop of Blue Limestone and general character of its replacement in 

 the Long and Derry mines and the great thickness of the White Porphyry 

 above it (the cross-cutting of the lower sheet of White Porphyry must 

 have occurred in the part eroded off) ; the transverse dikes of Gray Por- 

 phyry, and the intrusive sheets of Green Porphyry between the White 

 Limestone and Lower Quartzite; and, west of Mike fault, the outcrops of the 

 Blue Limestone shown in the Hoodoo and Echo shafts, and the supposed 

 form of the body of Josephine Porphyry, between it and the overlying 

 White Porphyry. The depth assigned the contact adjoining the Mike fault 

 may be too great, as in the previous section, since it is possible that the beds 

 rise toward an anticlinal fold. In the actual plane of the section the Lake 

 beds are not shown to reach as high up as they do on Section H; but their 

 extent on a line immediately north and south of this plane would be equal 

 to that of the former. West of the Hoodoo outcrop is indicated the anti- 

 cline which forms the southern continuation of the Dome fault, beyond 

 which a syncline must exist, as an extension of the synclinal basin proved, 

 to the north; but what portion of the synclinal beds involved in these folds 

 has escaped erosion is a matter of pure speculation. 



Perhaps the most suggestive teaching afforded by the north-and-south 

 sections is the graphic representation they give of the relative character and 

 amount of Glacial and Post-Glacial erosion. They afford successive cross- 

 sections of the various spurs represented on the map from the summit down 

 to the mesa below. Where Lake beds still exist, the rock surface below 

 them is the result of erosion in the earlier portion of the Glacial period. 

 The rock surface beneath the moraine material (r), whether in its original 

 ridges or rearranged, is probably practically the same as it was at the close 



