THE ADIRONDACK MOUNTAINS II 



City to five or six hundred feet at the northern end of Lake Cham- 

 plain, the elevation gradually increasing northward. Actual surveys 

 show that, in the Great Lakes region, a differential movement of 

 the land is now in progress, the elevation being greater toward the 

 north. Recent changes of level in the Adirondack district will be 

 described toward the close of the next chapter. 



Among other important processes which have long been active 

 in modifying the earth are those of weathering and erosion. 

 Weathering is brought about by the various atmospheric agencies 

 such as moisture, oxygen, carbonic acid gas, etc., together with 

 changes of temperature. The result is to cause all rock masses to 

 disintegrate or decay in the course of time. In this way most soils 

 are produced. In northern New York the original soils of this sort 

 have been very largely reworked and redeposited by the ice or by 

 streams of water in connection with the ice during the great Ice 

 Age. Were it not for the process of erosion, which includes both 

 the breaking up and removal of rock material, soils would be much 

 more widespread than they now are. Weathering prepares the 

 material which is carried away by the streams, and this material is 

 mostly deposited either along the flood-plains of the lower stream 

 courses, or on the bottoms of lal<es or oceans into which the streams 

 flow. Every stream, at time of flood, is heavily charged with mud 

 or even coarser sediment which has been derived from the wear 

 of the land of its drainage basin. The very presence of the sedi- 

 ment in the streams proves that the land is being lowered, and 

 although, on first thought, it may be supposed that no really great 

 change could be accomplished by this means, nevertheless we must 

 remember that nature has practically infinite time at her disposal 

 so that slowly but surely vast physical changes are wrought and, per- 

 chance, a tremendous canyon like that of the Colorado river in 

 Arizona may be carved out by erosion. The general tendency is 

 for all land masses to wear down to or near sea level and, were 

 it not for renewed earth movements, all lands, even including the 

 mountains, would be thus worn down to what is known as a pene- 

 plain condition. Northern New York was worn down to the con- 

 dition of a more or less well-developed peneplain at least twice 

 during its long history. Accordingly, that familiar expression " the 

 everlasting hills " is decidedly incorrect. 



Another important process is vulcanism, that is to say, igneous 

 activity in general. By this means materials are brought up from 

 within the earth to or near its surface. Thus an active volcano 



