GLACIERS 



I-'ii;. 135. Glaciers intermediate in type between cliff glaciers and valley 

 glaciers. Cascade Mountains, Wash. (Willis, U. S. Geol. Surv.) 



General Phenomena of Glaciers l 



. Dimensions. Some valley glaciers occupy only the upper parts 

 of mountain valleys, others extend through them, and push out on 

 the plain beyond. In length they range from a fraction of -a mile 

 to many miles. Their thickness is usually measured by scores or 

 hundreds of feet rather than by denominations of a larger order, 

 but the variation is great. The minimum thickness is that which is 

 necessary to cause movement, and this varies with the slope, the 

 temperature, and other conditions. There is also much variation 

 in the thickness in different parts of the same glacier. As a rule, it 

 is thinnest in its terminal portion, and thickest at some point be- 

 tween its terminus and its source. Cliff and reconstructed glaciers 



1 The following list includes some of the more available articles and treatises 

 >n existing glaciers; others are referred to in the following pages. 



Alaskan glaciers: Reid, (i) Nat. Geog. Mag., Vol. IV, pp. 19-55; ( 2 ) Sixteenth 

 Ann. Kept., U. S. Geol. Surv., Part I, pp. 421-461. Russell, (i) Nat. Geog. Mag.. 

 Vol. Ill, pp. 176-188; (2) Jour, of Geol., Vol. I, pp. 219-245. 



Gl,i,i,-rs in the I'nitcd States: (i) Russell, Eighteenth Ann. Rept., U. S. Geol. 

 Surv., Part II, pp. 379-409; (2) Glaciers of North America. 



Greenland glaciers: Chamberlin, Jour, of Geol., Vol. II, pp. 768-788; Vol. 

 III. pp. 61-69, 198-218, 469-480, 565-582, 668-681, and 833-843; Vol. IV, pp. 582- 

 592. Salisbury, Jour, of Geol., Vol. IV, pp. 769-810. 



