508 ALLEN DAVID HOLE 
Colorado,” pp. 216-26, evidences of glaciation at a number of points in the San 
Juan Mountains. These evidences include roches moutonnées, grooved and 
striated rock in place, shallow lakes, and glacial drift in the form both of 
scattered erratic bowlders and moraines. As to the time relations involved, Dr. 
Endlich concludes (1) that at least one glacier, called by him the Conejos, was 
not older than late Tertiary time, and might be much more recent, basing his 
conclusion on the relation of its action to the basaltic lava flows; and (2) that 
the glacier which descended the Animas valley was of older date than those 
whose effects were to be seen near the headwaters of the different streams 
named. He does not, however, seem to mean that there were two separate 
stages of glaciation. The total work done by glaciers in modifying the pre- 
glacial topography he considers to have been slight; aside from this no estimate 
is made as to the amount of glacial erosion, amount of ice, or area covered 
when the ice was at its maximum. 
1883. R. C. Hills —In the Proceedings of the Colorado Scientific Society, 
Vol. I, in an article entitled “Extinct Glaciers of the San Juan Mountains,” pp. 
39-46, Mr. Hills cites evidences of glaciation from numerous points, and 
makes certain estimates as to the extent of the ice and the time relations 
involved. The following summary shows the more important points presented: 
1. The ice attained a greater thickness and covered an area many times 
more extensive on western than on eastern slopes. 
2. Glaciers were not confined to existing valleys, but at some remote 
period probably the entire western slope of the mountains, except perhaps the 
higher peaks, was covered with an unbroken sheet of ice. As evidence support- 
ing this conclusion he mentions (a) the presence of large granite bowlders 
distributed 5 miles west of Durango; (0) erratics of eruptive rocks on mesas 
flanking the San Miguel River 35 miles from the source of the river; and (¢) 
erratic bowlders within a short distance of Montrose. 
3. The Animas Glacier was 1,200 to 1,500 feet thick “between Elbert and 
Silverton,” and nearly 3 miles wide ‘‘a short distance above Elbert.” 
4. During the period of extension of the ice sheet the erosion of Upper and 
Middle Cretaceous rocks amounted to 200 to 500 feet. 
5. Box canyons 50 to too feet deep have been eroded since the retreat of 
the local glaciers as in the Uncompahgre valley at Ouray and in the Animas 
valley above Elbert, etc. 
6. The total extent of the old ice envelope is estimated at more than 4,500 
square miles. 
1893. George H. Stone—In Vol. I of the Journal of Geology, pp. 471-75; 
Mr. Stone describes glacial phenomena found in the valley of the Las Animas 
River, and in some of the valleys tributary to it above Silverton. The moraines 
near Durango are noted, but the difference in age between the drift on the edge 
of the mesa lying east of the city and that lying near Animas City but little 
above the level of the river seems not to have been recognized. The total 
length of the Animas Glacier is given as about 70 miles, average slope of upper 
