154 FALLING OF GLACIERS. 
To these causes we might add the falling of gla- 
ciers in Alpine countries. These are large bodies of 
ice found in elevated districts, above the line of con- 
gelation. These are continually descending to- 
wards the valleys ; and they assist in the degrada- 
tion of the land by breaking away fragments from 
the rocks, and transporting all the loose substances 
with which they come into contact. There are, 
therefore, usually found in the front of glaciers 
heaps of rocks and trees, which have been driven 
before them in their course. Sometimes they trans- 
port blocks of large dimensions, which could not 
otherwise have been forced into the valleys. 
Such are some of the chief agents concerned in 
the destruction of rocks and the other solid portions 
of the globe ; we are now prepared to consider the 
eompensating powers of renovation. 
CHAPTER XV. 
AGENTS WHICH FORM ROCKS. 
Quantity of Sediment in River-water. — In the Rhine — In the 
Yellow Riv«r— In the Ganges.— Deltas.— Delta in the Lake 
of Geneva— Lake Mareotis— North American Lakes.— Delta 
of Inland Seas— Of the Rhone— Of the Po— Of the Nile— Of 
the Ganges— The Mississippi. 
We have seen that various causes are in contin- 
ual operation to break down the solid parts of the 
earth's surface ; let us now inquire what becomes 
of all these fragments. As there is no loss of mat- 
ter, it follows that there must be a reproduction, as 
well as a destruction, of the land. Indeed, where- 
ever water is found, there earthy deposites are go- 
ing on ; and the substance of all the strata which 
