RESULTS OF DYNAMIC MOVEMENTS. 35 



The uplift of the Mosquito Range was not the simple pushing up of the 

 beds into a monoclinal fold, as might appear at first glance from the seem- 

 ingly regular dip of the beds from the crest down it" eastern slopes, but a 

 somewhat irregular plication of them into anticlinal and synclinal folds, and 

 their fracturing by faults, which have the same general direction as the axes 

 of the 'folds without coinciding exactly with them, and which often pass 

 into folds at their extremities. The anticlinal folds have as a rule a very 

 steep inclination, sometimes nearly vertical, on the west side of the axis 

 and a more gentle slope to the east, thus approaching the form of the 

 isocline. It is along this steeper slope that the fracturing has generally 

 taken place, and the fault may thus follow the axis of a syncline or of an 

 anticline, according as it runs to the one side or the other of this steep slope. 



The north and south direction of the main crest of the range is evi- 

 dently determined by the great Mosquito fault, which, starting at some aa 

 yet unknown distance beyond the northern boundary of the map, follows 

 the foot of the steep slope west of the crest to the region of the Leadville 

 map, where for a short distance it bends somewhat further to the westward 

 and is thence continued southward in the Weston fault, which passes into a 

 synclinal fold south of Weston's pass. 



From the Mosquito fault just north of Mosquito Peak branches off the 

 next most important fracture plane, the London fault, which runs in a south- 

 easterly direction across the eastern spurs of the range. The line of this 

 fault passes just east of the axis of a most pronounced anticlinal fold across. 

 London Mountain and Pennsylvania hill to Sheep Mountain, on the side* 

 of which the folding can be most distinctly traced along the canon walls. 

 To the south of Sheep Mountain it apparently coincides with the axis of 

 the anticlinal fold which forms Sheep ridge, and with it gradually dies out 

 and passes under the level plain of the South Park. 



The geological structure of the Mosquito Range is simplest toward the 

 south and becomes more complicated as one goes north, reaching the ex- 

 treme of complexity opposite Leadville. Near Buffalo Peaks, a few miles 

 beyond the southern limits of the map, it seems to be a simple monoclinal 

 fold, the western slopes being entirely of Archean granite, and the crest 



