474 THE JOURNAL OF GEOLOGY. 



back to the sides of the valley. The largest of these lies on the 

 east side of the Animas river, between Animas City and Durango. 

 It is more than a mile in length, and the outer or distal side ends 

 in a bluff twenty to forty feet high. At its north and south ends 

 this curved terrace approaches near to the mesa bordering the 

 valley, thus enclosing a depression several hundred yards wide 

 that is occupied by a small lake in time of violent rains. A 

 basin of this kind could not have been hollowed out by the 

 river, and, besides, the terminal moraines of Animas City extend 

 across the north end of the basin. It is evident that this terrace 

 was formed laterally to the glacier in substantially its present 

 form. It contains great numbers of boulders up to fifteen feet 

 in diameter, but a large portion of it has been very much water- 

 rolled. The most probable interpretation is that -these higher 

 terraces began to be deposited at the outer edge as a lateral 

 moraine. Then as the ice gradually receded morainal matter 

 and glacial gravel were simultaneously deposited in the space 

 between the moraine and the retreating ice. This hypothesis 

 well accounts for the fact that morainal and water-rounded 

 matter are so intimately mixed in the terrace, also that the 

 overwash did not spread laterally back to the margin of the 

 valley. We thus have the terraces ending distally in the steep 

 slope characteristic of the moraine rather than the more gentle 

 slope of the overwash apron. Most of these higher terraces end 

 proximally (next the river) in rather steep slopes or bluffs rising 

 twenty to seventy-five feet above the lower terraces. No city of 

 Colorado has so much of glacial interest within its limits as 

 Durango, unless it be Leadville. 



It is an interesting fact that the cols of the mountain ridges 

 of this region are glaciated almost or quite to their tops. Thus 

 at Stoney Pass, the first pass north of Cunningham Pass, I saw 

 well -glaciated rocks within 200 feet (horizontally) from the top 

 of the pass. From the top of this pass the mountain slopes 

 steeply northwestward toward the Las Animas valley, and in 

 the opposite direction down the Rio Grande valley. The rocks 

 at the summit were weathered, and it was not evident whether 



