42 UNIVERSITY OF COLORADO STUDIES 



Absence of county lines, towns, government subdivisions, an3 other 

 useful data from early maps, vagueness in the designation of localities 

 in early reports, and unstable nomenclature of streams and mountains, 

 together with positive contradiction of maps by text in some instances, 

 have made it difficult accurately to locate some glacial areas without 

 a personal visit, which has been impractical. It seems certain, however, 

 that the work of ancient glaciers has been reported in at least twenty-two 

 of the fifty-nine counties of the state, as follows: Archuleta, Boulder, 

 Chaffee, Clear Creek, Conejos, Dolores, Gilpin, Grand, Gunnison, 

 Hinsdale, Lake, La Plata, Larimer, Montezuma, Ouray, Park, Pitkin, 

 Routt, San Juan, San Miguel, Summit, Teller. There are also some 

 remarks in the reports from which glaciation might be inferred in Custer, 

 Fremont, Huerfano and Saguache Counties, and it is, of course, entirely 

 possible that some reports may have been overlooked through faulty 

 indexing and cataloguing of the literature of the subject. The eastern- 

 most area is the Pike's Peak region, near the center of the state from 

 east to west, thus cutting out the entire eastern half of the state. The 

 areas in some of these counties are very hmited, in others more extensive; 

 but probably the glaciers did not extend over the whole surface of a 

 single county. These areas aggregate several hundred square miles. 

 In the Leadville region alone a single party has somewhat carefully 

 studied 250 square miles of glaciated territory,' and it is probable that 

 in the Arapahoe and Long's Peak region there are at least 500 square 

 miles of glaciation, practically continuous; but the aggregate is small 

 compared with the total area of the state, about 103,925 square miles. 

 It is not at all likely that all of the areas have yet been reported, and 

 certainly few have been exhaustively studied. Probably a careful 

 examination would reveal some evidence of glaciation in the vicinity 

 of all mountains in Colorado which rise above 12,000 feet, and at least 

 one place is reported where a glacier originated at an altitude of 11,000 

 feet. They generally occupied pre-existing valleys, changing the cross- 

 sections from the V-shape characteristic of rapid stream erosion to the 

 U -shape of glacial valleys, their work being confined to modifying rather 

 than making valleys. Some of them reached a length of twenty miles 



" Jour. Gcol., Vol. XII (1904), p. 698. 



