256 GEOLOGY. 



able, and the latter descends but little below the snow-line. In many- 

 cases it does not even enter the narrow valley which leads out from 

 the depression occupied by the snow-field. Such a glacier is nestled in 

 the face of a chff, and may therefore be called a cliff glacier ^ (Figs. 233 and 

 234). The snow-field of a cHff glacier is sometimes no more than a great 

 snowdrift, accumulated through successive years. CUff glaciers are 

 often as wide as long, and are always small, and between them and 

 valley glaciers there are all gradations (Fig. 235). Occasionally the 

 end of a valley glacier, or the edge of an ice-sheet reaches a precipitous 

 cliff, and the end or edge of the ice breaks off and accumulates like 

 talus below. The ice fragments may then again become a coherent 

 mass by regelation, and the whole may resume motion. Such a glacier 

 is called a reconstructed glacier. The precipitous cliffs of the Green- 

 land coast furnish illustrations. 



Of the foregoing types of glaciers, the ice-caps far exceed all others 

 bolh in size and importance, while the valley glaciers out-rank, in the 

 same respects, the other types; but since the valley glaciers are the 

 most familiar type, the general phenomena of glaciers will be discussed 

 with primary reference to them. 



THE GENERAL PHENOMENA OF GLACIERS. ^ 



Dimensions. — Glaciers which occupy valleys leading down from 

 snow-fields sometimes reach the upper parts of the valleys only, some- 

 times extend through them, and sometimes push out on the plain be- 



^ Jour, of GeoL, Vol. Ill, p. 888. 

 ^ ' The following list includes many of the more available articles and treatises on 

 existing glaciers; others are referred to in the following pages, 



Alaskan glaciers: Reid, (1) Nat. Geog. Mag., Vol. iv" pp. 19-55; (2) Sixteenth Ann. 

 Rept.,U. S. Geol. Surv., Part I, pp. 421-461. Russell, (1) Nat. Geog. Mag , Vol III 

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



Glaciers in the United States: Russell, (1) Fifth Ann. Rept., U. S. Geol. Surv,, pp. 

 309-355; (2) Eighteenth Ann. Rept., U. S. Geol. Surv., Part II, pp, 379-409;' (3) 

 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. Ill, pp. 875-902, and Vol. IV, pp. 769-810. 



Glaciers in general: Shaler and Davis, Illustrations of the Earth's Surface; Forbes, 

 Norway and its Glaciers, and Theory of Glaciers; Heim, Handbuch der Gletscher- 

 kunde. 



