LAS ANIMAS VALLEY. 341 



system of deep valleys bordered by mountains rising to elevations of from 

 11,000 to 14,000 feet. Over the upper part of this valley, covering 500 

 square miles, the precipitation is probably greater than over any other 

 equal area in Colorado. Every cirque and lateral valley contained its 

 glacier, which was tributary to that of a main valley. 



The rocks of this region are largely volcanic, and in general weather 

 easily, either by chemical decomposition or by fracture. Glacial scorings 

 are seldom found on exposed rock surfaces. Excavations made in con- 

 structing roads over the mountain passes and to the mines show that in the 

 larger cirques and passes the rock is glaciated up to about 12,000 feet. 

 Mining excavations have been made at higher elevations, but none of them 

 visited by me are in such situations that we could expect them to show the 

 glaciated rock. Hence, while it is probable that the glaciers extended nearly 

 or quite to the tops of the higher basins, I have as yet no glacial scratches 

 to prove it. 



The scratches in the lateral valleys are parallel with these valleys, but 

 as we descend them we come to where the scratches are parallel with the 

 main valleys and transverse to the lateral. Obviously if we can determine 

 the height above the main valleys that these scratches parallel with them 

 reach, we shall know the depth of the great valley glaciers. Such scratches 

 I have from time to time observed, and by degrees the upper limit was 

 raised, till now it is proved that the main Las Animas glacier was more than 

 1,000 feet deep at Silverton and at least 1,500 feet at a point 5 miles south 

 of Silverton. This was the main outlet of the ice of this region. The 

 tributary glaciers reached to the tops of cols 12,000 feet high, and perhaps 

 higher. Thus at Stony Pass, a pass from the Rio Grande over the Conti- 

 nental Divide to Las Animas Valley via Cunning-ham Gulch, I found well- 

 glaciated rock within 100 feet horizontally from the top of the pass, and 

 on both slopes. On each side were peaks of the range rising 1,000 feet or 

 more above the pass. It is thus proved that the flow took place from the 

 very top of the ridge down two valleys in opposite directions. The supply 

 probably came laterally from the adjacent peaks. 



Nowhere in these steep mountains have I found jjromineut lateral 

 moraines in the form of ridges or terraces. Many of the slopes are so steep 

 that no moraine stuflf could remain perched on them. The volcanic rocks 

 have often weathered and formed slides of talus 1,000 to 2,000 feet high. 



