RELATIONS OF DISINTEGRATION AND DECOMPOSITION. 499 



tegration at high latitudes also follows from the low temperature, because 

 very unfavorable to chemical action and to abundant organisms. 



Therefore in regions of high latitude the rocks are ordinarily broken 

 down and not greatly changed chemically. The exceedingly rapid and 

 extended disintegration of the rocks in regions of high latitude is well 

 illustrated by such countries as Greenland, Spitzbergen, Franz Josefs 

 Land, etc. As in the arid regions, the sedimentary rocks formed in regions 

 of high latitude may be composed of disintegrated materials, chemically 

 essentially like the materials from which the rocks are derived. As in the 

 arid regions, where mechanical materials from different sources are mingled, 

 they represent the average composition of the original rocks rather than 

 any one original rock. 



Regions of marked topographic relief. — Regions of marked topographic relief are 

 usually regions of considerable elevation. In such regions the mechanical 

 forces work under most favorable conditions. Gravity pulls the material 

 down the steep slopes. The range in temperature is great; water alter- 

 nately freezes and thaws; glaciers are prevalent. Consequently material 

 is split or ground from the solid rocks and- is carried by gravity in great 

 quantity to lower levels. 



The remarkable effect of elevation and sharp relief in disintegration 

 is especially well illustrated in high mountain ranges. In such regions 

 great and small masses are split from the cliffs by the disintegrating forces 

 and agents or are carved from the valley floors by the glaciers, and are 

 transported to a lower level by water or by ice with scarcely appreciable 

 chemical change The cirques at the heads of glaciers give excellent 

 illustrations of the very great rapidity of disintegration due to the combi- 

 nation of the above causes. The Matterhorn, with its sharp triangular 

 peak and the great cirques at its base, is a most impressive illustration of 

 such disintegration. The peaks of the High Sierras and the Canadian 

 Rockies afford many fine illustrations of the same process. 



Penck suggests that the average altitude of mountains in any given 

 region for a given kind of material is limited by the fact that disintegration 

 increases so rapidly as the height increases that for any given area there is 

 a height where the forces of disintegration degrade the mountains as fast as 

 the forces below are able to lift them.' 1 



« Penck, A., Morphologie der Erdoberfliiche, J. Engelhorn, Stuttgart, 1894, pt. 2, pp. 334-335. 



