176 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



beds, which will be described later. The Archean area, with its covering' 

 of Lake beds on the lower spurs, extends north as far as Empire gulch, 

 but beyond that line it no longer outcrops, except where brought to the 

 surface by faulting and erosion in the deep amphitheaters near the crest of 

 the range. 



Weston fault. From Weston's pass northwestward the Weston fault 

 follows the foot of the steep western slope of the main crest of the range, 

 approximately parallel to and a little east of the valley bottoms of the two 

 forks of Weston's Creek. East of it are Archean exposures, capped, either 

 on the crest of the range or on its eastern slopes, by easterly dipping Pale- 

 ozoic beds. To the west is a fringe of successive outcrops of the same 

 beds, also dipping regularly eastward, whose varying outlines, as shown on 

 the map, are entirely due to the relative depth of erosion of the various 

 gulches Were the structural conditions studied on a single transverse line 

 in this area they would be naturally supposed to be those of a simple 

 monoclinal fault; but the unmistakable evidence of the synclinal fold, as 

 already described on Weston's pass, and the conditions found on Empire 

 Hill, which will be described below, show that before erosion had removed 

 it there must have been a fold somewhat as indicated by the dotted lines in 

 Section G, Atlas Sheet IX. From the pass down the south branch of 

 Weston's Creek nearly to the forks, the Lower Quartzite extends up the west 

 slopes of the valley, while the Blue Limestone forms a decided shoulder on 

 the eastern slopes ; the White Porphyry body, which is only about twenty 

 feet thick at the pass, thickens to the northward and by its white color 

 forms a prominent feature in the landscape. 



Just above the forks the north branch of Weston's Creek runs in a 

 narrow ravine, in which the dip of the beds is somewhat steeper than in the 

 south branch, which may be explained by its proximity to the fault line. 

 On the northwest side of. this ravine the Paleozoic beds sweep up on a 

 broad flat shoulder, which forms the southern continuation of I^mpire Hill, 

 gradually assuming a shallower dip as they extend farther westward. 



Empire Hiii. This name is given to the upper part of the spur between 

 Weston's and Empire gulches and the broad shoulder or secondary ridg-e 

 lying between the branches of these gulches and the head of Union gulch. 



