GLACIATION IN THE TELLURIDE QUADRANGLE 509 
surface 83 feet or more per mile, thickness near Silverton, 1,500 feet. Attention 
is also called to certain facts, viz.: (1) that striations on rock in place are 
relatively rare on account of the character of much of the outcropping volcanic 
rock; (2) that a comparatively small amount of morainal material is to be 
found; and (3) that the amount of outwash gravels in the form of terraces and 
valley train is large. 
1899. George H. Stone-—In Monograph 34, U.S. Geological Survey, pp. 340- 
4s, Mr. Stone repeats substantially what was published in the Journal of Geology 
in 1893 in regard to glacial phenomena in the valley of the Las Animas, and 
adds notes on evidences of glaciation in other valleys of the San Juan Moun- 
tains, viz., the San Miguel, Uncompahgre, and upper Rio Grande; and men- 
tions as glaciated the upper parts of the valleys of Los Pinos, San Juan, Navajo, 
Chama, and other rivers of the western slopes of the mountains. Moraines, 
erratic bowlders, roches moutonnées, and outwash gravels are mentioned, and 
locations are given for some of the best-marked instances of such phenomena. 
1899. Whitman Cross—In the Telluride Folio, p. 15, Mr. Cross records 
evidences of glaciation as follows: (1) in the upper parts of some valleys, roches 
moutonnées, striated and polished rock in place, small lake basins, and glacial 
cirques; (2) at lower elevations in the principal valleys and on some ridges, 
glacial deposits consisting of angular and subangular bowlders, gravel, sand, 
and finer material, sometimes in the form of small moraines, sometimes in 
isolated patches scattered over the surface. The largest area of drift mapped 
lies east of the Lake Fork of the San Miguel River and is referred to the action 
of a stream of water which, at a time when the ice moving down Lake Fork 
was higher than the canyon walls, was believed to flow during the summer in a 
channel along the eastern side of the glacier to join the main fork of the San 
Miguel River near Keystone. Aside from a suggestion that ice from Lake 
Fork seemed to be present at a later date than in the main fork above Key- 
stone, the time relations are not discussed. 
1900. Arthur Coe Spencer.—In the Twenty-first Annual Report of the United 
States Geological Survey, pp. 156-59, Mr. Spencer names as evidences of glacial 
action in the Rico Mountains (1) certain topographic features, (2) a few 
instances of polished and striated bed rock, and (3) some deposits of glacial 
débris. He concludes that the amount of ice present was small, and that the 
time covered by glacial conditions in this group of mountains was short. 
1905. Whitman Cross.—In the Rico Folio, pp. 6, 12, and 13, the evidences 
of glaciation named by Mr. Cross are much the same as those named by Mr. 
Spencer in the work last cited; there is added, however, a suggestion of two 
distinct glacial stages, viz.: (1) a recent stage referable to the close of the 
Wisconsin period, and (2) a pre-Wisconsin stage. The morainal deposits, 
roches moutonnées and striae, are referred to the former; high-level bowlder 
beds are classified as pre-Wisconsin in age though not necessarily glacial in 
origin. 
1905. Whitman Cross.—In the Needle Mountains Folio, pp. 6, 11, and 12, 
