38 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



many anticlinals and synclinals, in which the prevailing dip of the beds is 

 to the eastward and the throw of the faults is mainly an uplift to the east. 



The area west of the Mosquito fault and north of the Leadville region 

 is mainly occupied by beds of the middle member of the Carboniferous and 

 by porphyry sheets, flexed into gentle folds of varying directions, but appar- 

 ently not broken by faults. This region is already at some distance from 

 the ancient shore line, which is marked by the outcrops of Cambrian and 

 Silurian beds. These bend to the westward around the head of Tennessee 

 Park, and reach well up on the north slopes of the Sawatch in the Eagle 

 River region; but, while the sedimentary beds bend thus in general strike 

 to the westward, the Mosquito fault and the crest of the range which has 

 been uplifted by its movement continue on unchanged in their trend. 



North of Mosquito Peak is a large area in the higher part of the range, 

 including the splendid amphitheaters in which the Platte and Arkansas 

 Rivers rise, where the overlying Paleozoic beds have been entirely removed 

 and only Archean exposures, traversed by dikes of earlier eruptive rocks, 

 now remain. 



East of this area the flanks of Loveland hill and the massive of Mounts 

 Bross and Lincoln are occupied by easterly dipping Paleozoic beds, which 

 evidently are the eastern member of a broad anticlinal fold ; but of the 

 actual structure of the beds which once arched over the Archean area 

 there is nothing left to tell. It is probable that there were folds here simi- 

 lar and more or less parallel to the Sheep Mountain fold, as has been indi- 

 cated in a general way by the dotted lines in the sections which cross this 

 region. A partial proof of this is afforded by a deep synclinal adjoining Mos- 

 quito fault on the west, somewhat similar to that on Weston's pass, which 

 is found at the base of Bartlett Mountain, at the northern edge of the map; 

 its axis has more westerly direction than the plane of the fault. In this 

 northern area there is also a great development of earlier eruptive rocks 

 as contrasted with the southern half of the region, though they have less 

 relative importance than in the middle zone, which includes the immediate 

 vicinity of Leadville. The greater proportion of these bodies are in the 

 form of intrusive sheets, interstratified with Paleozoic beds; but the dike 

 form is also found, more especially in the Archean exposures in the ampin- 



