154 GEOLOGY AND MES'ING INDUSTRY OF LEADViLLE. 



anticlinal fold ovei- the Archeau are very distinct, the jjanially eroded Blue 

 Limestone forming the present crest of the ridge. 



On the south end of White Ridge, in the angle at the junction of Four- 

 Mile amphitheater with the main gulch, is a prominent outcrop of dark-blue 

 limestone, standing at an angle of 45^, directly above the porphyry. A 

 short distance to the west of this outcrop, at the foot of the steep slope 

 and at intervals along the southwest side of White Ridge, on a line rising 

 gradually as it approaches the head of P'our-Mile amphitheater, prospectors 

 with their keen natural instinct have traced the same bed under the heavy 

 talus slopes of ddbris which cover it. 



In the very bottom of the Four-Mile amphitheater, as shown on the 

 map, the Blue Limestone again outcrops in the bed of the gulch, and has 

 been developed in the important Badger Boy mine, and by numerous pros- 

 pect holes. On the ridges around. White Porphyry forms the surface, whic-h 

 is in its normal position above the Blue Limestone. The line of the Blue 

 Limestone, traced along the face of White Ridge, is however at a consid- 

 erable distance above the actual level of the Badger Boy limestone, and at 

 a still greater distance geologically, inasmuch as the normal dip is to the 

 east. It is therefore evident that the limestone under White Ridge has 

 been lifted up by a fault, as shown in Section F, Atlas Sheet IX. The 

 White Porphyry forming the mass of White Ridge is there in its normal 

 position above the Blue Limestone, except at the south end just mentioned, 

 where occur the prominent outcrops of dark limestone shown in the fore- 

 ground of the sketch. The thickness of stratified beds exposed at this point 

 is between 150 and 200 feet, the upper members of which have the character- 

 istics of Blue Limestone, while toward the base are light-colored silicious 

 beds, largely of white quartzite. Although the lithological character of the 

 beds does not correspond in every respect with similar sections elsewhere, 

 there is no doubt that it represents the main body of the Blue Limestone, and 

 very probably the Parting Quartzite with a portion of tlie White Limestone 

 beneath it. This heavy belt of dark limestone does not extend very far up 

 the ridge, but gradually thins out and disappears, the sedimentary beds 

 adjoining the porphyry at the summit of White Ridge being quartzites and 

 micaceous shales of the Weber Grits series. It is evident, therefore, that 

 the White Porpliyr}' mass here cuts diagonally up across the beds, and that 



