50 



AQUEOUS AGENCIES. 



be even above it — Dana), but diverges as we pass toward the pole, 

 and finally touches the sea-level at about 66° north and south latitude, 

 at ~b b. Below this, again, is the line of lower limit of glaciers, which, 



commencing again 

 nearly coincident with 

 the two preceding, at 

 the equator, approach- 

 es and touches the sea- 

 level at about 50° lati- 

 tude, or, under favor- 

 able circumstances, at 

 even lower latitudes. 

 The difference be- 

 tween these lines is 

 often several thousand 

 feet. In the Alps, the 

 line of 32° is 2,000 feet, 

 and the line of lower 

 limit of glaciers 5,000 

 feet, below the snow- 

 line. In some parts 

 of the arctic region, 

 the line of 32° is 3,500 

 feet below the snow-line, and in Norway the lower limit of glaciers 

 is 4,000 feet below the line of 32° (Dana). For the sake of simplicity 

 we have represented the surfaces, of which these lines are the sections, 

 as regular spheroids ; but, in fact, they are very irregular, being much 

 influenced by climate. Their intersection, with the sea-level will, 

 therefore, not be along lines of latitude, but will be irregular, like iso- 

 therms. As the line a c marks the lower limit of glaciers in different 

 latitudes, it is evident that at c glaciers will touch the sea, and beyond 

 this point will run far into the sea. It is in this manner, as we will see 

 hereafter, that icebergs are formed. In Chili, glaciers touch the sea- 

 level at 46° 40' south latitude.* 



General Description. — In glacial regions a mountain-valley is occu- 

 pied in its highest part by perpetual snow ; below this, farther down 

 the valley, by neve — a granular snow, intermediate between snow and 

 ice ; still farther down, by true glacier-ice ; and, finally, by a river (Fig. 

 44). This river is formed partly by the melting of the whole surface 

 of the glacier, both above and below, and partly by the natural drain- 

 age of the valley. The glacier, however, is the principal source. From 

 the point of every glacier, therefore, runs a river. 



Fig. 39. —General Relation of Limit of Glaciers to Snow-Line. 



* D'Arcbiac, Histoire de Geologic 



