Page:The Journal of geology (IA journalofgeology11893univers).pdf/49

the top of the ridge had been glaciated, but it is certain the ice or snow flowed in opposite directions from the col. On each side of the pass, peaks of the Continental Divide rise above the col to a height of 1000 to 2000 feet. It is evident that the snow from these peaks would flow or slide from each side down into the pass, and maintain a supply of névé or ice right on top of the ridge in the pass. The pass is about 11,800 feet high. It thus appears that the snow fields reached nearly to the tops of the mountains, say about 12,000 feet in the cirques and passes, while above this the discharge was probably in large part by avalanches.

Durango city is situated in about N. Lat. 37° 16′, a few miles north of the end of this glacier. It is to be carefully noted, in the study of the climates of the glacial epoch, that a glacier nearly seventy miles long reached so far south. Apparently the most snowy part of Colorado now was also the most snowy then.

During the retreat of this glacier it left numerous small retreatal moraines, both in the main valley and in the tributary valleys above Silverton. One of the most accessible is near the junction of the two branches of Mineral creek, about three miles northwest from Silverton.

It is noticeable that the proportion of moraine stuff left by this glacier is small as compared to the glacial sediments. Nowhere have I yet found very noticeable ridge or terrace lateral moraines. This is in part due to the steepness of the hills that border the sides of the Animas valley. There is usually a scattering of glaciated matter on these hill slopes, and where they are less steep, or in ice of ridges projecting out into the valley, local morainal sheets are sometimes found that have a depth of twenty feet or more. Small terrace-like lateral moraines extend for a mile or two north of the terminal moraines of Animas City near Durango. Probably the snow avalanches and flowing névé carried down débris and incorporated it with the glacier proper, so that there were no large surface lateral moraines as in some of the valleys of the Alps, or in the Arkansas and some other valleys of Colorado. In other words, the débris of this glacier was largely englacial and basal.