36 GEOLOGY AND MIMNG INDCJSTEY OF LEADVILLE. 



formed by Cambrian quartzites dipping genth' eastward and resting uucon- 

 formably on the Archean. 



At the southern edge of the map an anticHnal and synclinal fold comes 

 in to the east of the monocline. Here the range has a double crest en eche- 

 lon, divided by the longitudinal valley of Weston's pass, which runs north- 

 west magnetic following the direction of the strike. The i-idge of South Peak 

 to the west of the pass is formed by a monocline of easterly-dipping Cam- 

 brian and Silurian beds. The valley of the pass itself is formed by a com- 

 pressed synclinal fold in Carboniferous strata, along the eastern side of 

 which runs the Weston fault, bringing up the Aix'hean and Cambrian on 

 its east side. The ridge bounding the valley on the east, which is the south- 

 ern end of the main crest of the Mosquito Range, is an eroded anticlinal 

 fold, from whose crest tlie overlying Paleozoic strata have been almost en- 

 tirely removed, leaving the core of Archean exposed. < )n the very sum- 

 mit of Weston's Peak a small patch of Cambrian (juartzites is left, a remnant 

 of the crest of this fold, and at its western base the same beds are found in 

 a vertical position adjoining tiie fault, while on the more gentle slopes of 

 the eastern s])urs are found the regular succession of easterh--dipi)ing Pale- 

 ozoic beds belonging to the eastern member of the anticline. The ridge 

 sinks to the southward, and over its southern end the arcli of Paleozoic beds 

 is still left entire, but the anticlinal fold also sinks to tlie southward and 

 entirely disajijiears beyond the limits of the map. 



The same general structure continues northward as far as Empire Hill, 

 but a short distance from the southern edge of the map a second anticlinal 

 fold, that of Sheep Eidge, comes in at the extremity of the eastern slope of 

 the range, while from its steep western slope erosion has removed all trace 

 of the synclinal fold seen on Weston's pass, leaving onh- the easterl3^-dip- 

 ping Paleozoic beds belonging to the monocline on the west of the fault, 

 and the Archean on its east side ; the crest of the range is formed of east- 

 erly-dijiping Paleozoic beds, or, where these have been eroded away, by 

 Archean schists and granite. This double anticlinal structure is best shown 

 in Section G (Atlas Sheet IX), which is drawn at right angles to the strike, 

 and in which the supposed form of the eroded synclinal is sliown by dotted 

 lines. The line of this section also crosses two secondary anticlinals or 



