28 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



denly changes, and from sharp serrated ridges they become broad, gently 

 sloping mesas or table-lands. On the eastern side, though the descent into 

 the glacial amphitheaters is almost as precipitous, the average slope is much 

 less steep, and the spurs as a rule descend in long sweeping curves, widen- 

 ing out gradually as they approach the valley. 



The spurs on either side of the range are thickly covered with a forest 

 growth of alpine character, reaching from the valleys of the streams up to 

 an average altitude of 11,700 feet, the upper limit varying somewhat with 

 the more or less favorable conditions of the surface, and extending appar- 

 ently somewhat higher on the western than on the eastern slopes. 



In the northern portion of this area, between the heads of the Arkan- 

 sas and Platte Rivers, the main crest of the range, which has hitherto fol- 

 lowed an almost straight line, takes a bend en echelon, and is continued on a 

 line removed about two miles to the eastward, resuming, however, its orig- 

 inal line just beyond the limits of the map. The massive formed by the 

 three peaks, Mounts Cameron, Bross, and Lincoln, the last the highest point 

 within the area mapped, lies still to the eastward of this crest and is topo- 

 graphically an almost independent uplift. Sheep Mountain and the ridge 

 which extends southeastward from it also form an apparently abnormal 

 feature in the topography of the eastern slope. 



The sketch given in Plate III shows the general outlines of the eastern 

 slopes of the Mosquito Range and the basin of the South Park, as seen 

 from a western spur of Mount Silverheels. The sky-line of the western half 

 is the crest of that portion of the range included in the map which lies south 

 of Mosquito Peak, the low gap is that of Weston's pass, beyond which is 

 the Buffalo Peaks group. The various gulches south of the Mount Lin- 

 coln massive are indicated by name, and the lines of outcrop on their 

 walls are somewhat strengthened to show the geological structure, which 

 will be explained in detail in Chapter IV. Buffalo Peaks are 25 miles 

 distant from the point of view, and the volcanic hill in the extreme left- 

 hand corner of the sketch, seen across the South Park plain, is over 40 

 miles distant. The little hill on the edge of the plain, and on a line with 

 the eastern spur of Buffalo Peaks, which forms the continuation of the 

 Sheep Mountain ridge, is Black Hill, which lies just beyond the extreme 



