RESULTS OF DYNAMIC MOVEMENTS. 37 



minor waves in the strata, which are the almost invariable accompaniments 

 of the larger folds. 



In this southern area the older eruptive rocks are but little developed, 

 their only representative being a thin but persistent sheet of White Por- 

 phyry above the Blue limestone. This increases in thickness from about 

 fifty feet at Weston's pass to over a thousand feet at its supposed source in 

 White Ridge, on the north side of Horseshoe gulch. 



In the middle region of the area mapped, through an east and west 

 zone which includes the principal mines of Leadville and vicinity, the de- 

 velopment of bodies of earlier eruptive rocks is so great that the structure 

 of the sedimentary beds is obscured and not always easy to trace. On the 

 eastern slopes the double anticlinal structure continues as far north as Mos- 

 quito Peak, at the head of Mosquito gulch. The great Sheep Mountain fold, 

 with the London fault cutting through its steeper western side, gradually 

 converges toward the crest of the range. Views of the sections of this 

 fault-fold afforded by the canons of Horseshoe and Big Sacramento gulches 

 are seen in Plates XV, XVI, and XVIII. East of this fold the strata 

 slope gently eastward, with a slight secondary fold traceable along the 

 extreme foot-hills. Between the Sheep Mountain fold and the crest of the 

 range the strata of the gradually narrowing syncline are cut across by 

 the two great eruptive bodies of White Porphyry and of Sacramento Por- 

 phyry, in White Ridge and Gemini Peaks, respectively, which are accom- 

 panied by a slight displacement. The nearly horizontal Paleozoic beds 

 forming the crest and eastern member of the main anticline extend some- 

 what to the west of the topographical summit of the range, but the western 

 member of the anticline and the succeeding syncline (if it extended so far 

 north) are either removed by erosion or buried beneath sheets of porphyry^ 



On the western slopes in this zone the sedimentary strata, now greatly 

 augmented in thickness by interstratified sheets of porphyry and extend- 

 ing nearly to the valley of the Arkansas, are flexed into a number of minor 

 folds and broken by many shorter faults, most of which pass at either end 

 into anticlinal or synclinal folds. This is the area which is included in the 

 detail map of Leadville and vicinity and which is described at length in 

 Chapter V. It is traversed by seventeen larger and smaller faults and has 



