30 THE PRINCIPLES OF AGRICULTURE 



26a. The wearing away of rock by the weather may be ob- 

 served wherever stones are exposed. Even granite and marble 

 monuments lose their polish and luster in a few years. The 

 sharp and angular projections disappear from the ledges and 

 broken stones of railway cuts and quarries. The pupil should 

 look for the wear on any rocks with which he may be familiar. 

 All stones tend to grow smaller. On a large scale, the wasting 

 of rocks may be seen in the debris at the base of precipices and 

 mountain peaks (Fig. 1), or wherever steep walls of rock are 

 exposed. The palisades of the Hudson, and other precipitous 

 river and lake bluffs, show this action well. Mountains tend to 

 become rounded in the long processes of time, although some 

 rocks are of such structure that they hold their pointed shape 

 until worn almost completely away. In Geikie's "Geological 

 Sketches," Essay No. 8, the reader will find an interesting 

 account of weathering as illustrated by the decay of tombstones. 



26b. The extent of this weathering and denuding process in 

 the formation of soils may be graphically illustrated by the pres- 

 ent conformation of the Alps and adjacent parts of Europe. 

 Lubbock writes that "much of the deposits which occupy the 

 valleys of the Rhine, Po, Ehone, Reuss, Inn, and Danube — the 

 alluvium which forms the plains of Lombardy, of Germany, of 

 Belgium, Holland, and of southeast France — consists of materials 

 washed down from the Swiss mountains." The amount of mate- 

 rial which has been removed from the Alps is probably " almost 

 as great as that which still remains." So great has been the 

 denudation that in certain cases "what is now the top of the 

 mountain was once the bottom of a valley/' The Matterhorn, the 

 boldest and one of the highest of the Alps, " is obviously a rem- 

 nant of an ancient ridge," and the "present configuration of the 

 surface [of Switzerland] is indeed mainly the result of denuda- 

 tion. * * It is certain that not a fragment of the original sur- 

 face is still in existence, though it must not be inferred that the 

 mountains were at any time so much higher, as elevation and 

 denudation went on together." There is even evidence to show 

 that an earlier range of mountains occupied the site of the 

 present Alps, and that these old mountains were removed or 



