EARLIER DRIFT DEPOSITS 263 



and in addition large crumbling blocks of the agglomerate itself. Xear 

 the ridge these deposits are covered by the debris of recent landslides from 

 the cliffs of the ridge. Except where obscured by landslide, the slopes 

 westward from Cimarron ridge have even grades of low slope, such as 

 are characteristic of a mature topography, but they have been materially 

 modified by a renewed activity of the streams draining them, and the 

 gravels are preserved in their original positions only on the divides and 

 ridges between the intrenched streams. 



ORIGIN OF THE DRIFT 



The brief examination made failed to disclose any striated pebbles in 

 the material occurring on Horsefly and West Baldy, but there are other 

 sufficiently good reasons for believing that the deposits are of glacial 

 origin. 



The study of the material represented in the two occurrences shows 

 that it was derived from the high mountains to the south and from which 

 Horsefly peak is now separated by the broad and deep depression of the 

 Dallas drainage basin. A very large part of the material consists of late 

 volcanic rocks, now preserved only as remnants capping the highest sum- 

 mits, which are at some distance to the east. There are also numerous 

 boulders of intrusive porphyry which can have come only from Mears 

 peak, while there is a notable absence of the gabbro occurring on Mount 

 Sneffels and only a slight representation of the early braccias which con- 

 stitute a large part of the adjacent mountains. There can be no doubt 

 that the material covering West Baldy and Horsefly peak as well as that 

 composing the kame-like hill to the north was derived from the mountains 

 to the south or southeast ; but since its transportation from its source the 

 mountains have undergone extensive degradation, and the younger rocks 

 represented in the West Baldy and Horsefly gravels have been largely 

 removed and older formations exposed. 



Evidence has been found at the foot of the mountains that at various 

 points between the Uncompahgre river and the northwest end of the range 

 landslides occurred on an enormous scale before the dissection of the old 

 lowland, previously mentioned, had begun. The deposits of the old land- 

 slide material closely resemble more recent deposits of similar origin, but 

 the rough surface and peculiar topography characteristic of young slides 

 has been much softened and modified by age. Probably the most striking- 

 feature of this old landslide material and the best indication of its age 

 is the intimate relation it bears to the old topography and the absolute 

 independence of its position to the present-day topography. The material 

 occurs, beneath the comparatively smooth surface, in 'characteristically 



