HAXDEX.] 



GEOLOGY SOUTH PAKK. 39 



tlie east side of the park. They slope up close on to the east side of the 

 Park range, but the wash or drift from the mountains has so covered 

 the slope that the beds in contact with the Metamorphic rocks can sel- 

 dom be seen. 



Along- the valley of the Platte the drift-material, consisting mostly of 

 water- worn bowlders, is immense. The entire mass of drift-deposit, in 

 which the placer diggings are located, has been washed down from the 

 valleys of the little streams of the South Park. The local origin of 

 the drift, so far as our Eocky Mountain districts are concerned, is illus- 

 trated in a remarkable manner in the park. 



The area of the park is about 1,200 square miles ; its greatest length 

 is northwest and Southeast, about forty miles, and in the opposite 

 direction about thirty miles. The shape is elliptical. The general ele- 

 vation varies from 8,000 to 10,000 feet above the sea. The drainage is 

 from the northwest to the southeast. Before presenting any details of 

 the geology of the Park range I will state briefly what I believe to be 

 its relation to the great Sawatch range, on the west side of the Arkan- 

 sas Biver. I am of the opinion that the Park range is a portion of a 

 gigantic anticlinal, of which the Sawatch range is the central axis 5 that 

 the Park range is a portion of the east side of the Sawatch range, and 

 that the great valley of the Upper Arkansas is mostly the result of ero- 

 sion through the granite rocks. The eroding agents began their work 

 in a fissure produced by the uplift, but once a depression or opening 

 formed for the accumulation of water and ice, the work of disintegra- 

 tion would commence. The subject of earth-sculpture, or erosion, as it 

 is illustrated in myriad forms in the Eocky Mountains, and nowhere in 

 the West on a grander scale than in the mountains of Colorado, will be 

 touched upon frequently in this report, and will be treated more fully, 

 under a separate head, at some future time. 



The Park range is very irregular in elevation. Portions of it are low, 

 while several peaks rise about 14,000 feet. Mount Lincoln is 14,183 feet, 

 and upon the very summits are found the sedimentary rocks. The 

 action of the internal forces has been very irregular also, sometimes lift- 

 ing the granite nucleus up to an elevation of 12,000 to 14,000 feet in 

 the form of puffs, as it were, the sedimentary beds inclining at various 

 angles and in different directions from its sides. The aggregate inclina- 

 tion of the strata is plainly to the eastward, and the gentle slopes are 

 on the east side of the range, while on the west the sides are very ab- 

 rupt, and in some instances the rocks overhanging, so that the general 

 form or outline of the Park range would indicate that it might be 

 regarded as a portion of an anticlinal. 



All along the east side of the Park range are numerous gorges, which 

 extend down from the crest and gradually expand out into moderately 

 wide grassy valleys. Immediately after leaving the gorge, however, 

 the drift-material is very great, covering the valleys and lying high 

 upon the mountain-sides. These gorges usually commence near the 

 water-crest in a somewhat extended amphitheater, which is constantly 

 enlarged by the breaking down of the sides. These gorges all point to 

 a common origin, and have no doubt been carved out by the combined 

 action of water and ice. The morainal matter brought down by the old 

 glaciers is shown most abundantly in the lower portions of these gorges 

 as they expand out into the valleys that open into the plains. The evi- 

 dences of ancient glacial action are quite abundant all through the 

 Park range, but far more remarkable proofs are found in the Sawatch 

 range. These facts will be noted more fully in another place. 



From Fairplay we follow up the valley of the South Platte for ten 



