FOIIMER GLACIATIOX OF THE EOCKY MOUXTAIXS. 65 



the glaciers. These, however, did not descend anywhere in this region to 

 nearly as low a point as was reached by several of the Californian glaciers. 

 The upper part of the Arkansas Valley is about 9,000 feet above the sea- 

 level, and there is no proof that it was ever occupied by ice. Indeed, the 

 whole series of glacial phenomena in this part of the Rocky Mountains is con- 

 sistent with itself throughout ; only the highest summits and the most ele- 

 vated valleys were occupied by the ice. For instance, at the head of South 

 Park, at an elevation of neai'ly 10,000 feet, just above Fairplay, the valley of 

 the Middle Fork of the South Platte is barred across by an immense terminal 

 moraine, 150 feet high, above which was once a large lake, but which has 

 since been drained off by tlie cutting through of the detrital mass, the ma- 

 terial of which has been carried down and spread over the valley below by 

 the rush of water. Nowhere below this point could any traces of glaciation 

 be discovered over the whole area of the Park ; while above the moraine, in 

 all the adjacent higher side-valleys and canons, such indications were ex- 

 tremely conspicuous. The topographical features of the range above Fairplay 

 Avere highly favorable to the formation of an immense .glacier ; hence the 

 united stream of ice coming down this branch of the Platte was nearly or 

 quite equal to the largest of those formed on the eastern declivity of the 

 Sawatch Range, the breadth and height of which furnished all the necessary 

 conditions for the accumulation of "laciers of the largest dimensions. Whether 

 the western slope of the Sawatch Mountains was as favorably situated as the 

 eastern, in this respect, the writer is unable to state from personal observa- 

 tion. On the geological map of Colorado, published under the direction of 

 Professor Hayden, a large moraine is indicated as having its origin in the 

 canon between Mounts Harvard and Yale, and descending to the west, ter- 

 minating at an altitude of about 9,500 feet. No other moraines are shown 

 on the map in any of the ranges directly west of the Sawatch. To the 

 southwest of this, however, there are several. A small area is indicated as 

 covered by morainic debris at a locality on the head-waters of Vallecito 

 Creek, northwest of Mount Oso (13,640 feet). Another is shown at the head 

 of the Lake Fork of the Gunnison, in latitude 37° 56', at about 9,000 feet in 

 elevation. Besides these minor glaciated areas, there are two others of more 

 importance : one of these is near the .sources of the Rio Piedra, south of 

 Weeminucke Pas.s, on the southwest side of the San Juan Mountains, in 

 latitude 37° 30' ; the other at the head of Rio Chania, in latitude 37'. These 

 two last mentioned, which are of interest, since they appear to be the most 



