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POPULAR SCIENCE REVIEW. 
caverns, and displaying their action in a lesser degree in the 
fantastic shapes and hollows so often seen on the exposed sur- 
faces of limestone and other rocks. With rain, other atmo- 
spheric agencies must be noticed, such as frost, which acts 
forcibly in the disintegration of rocks, particularly those ex- 
posed in cliffs and ravines. Rain and frost thus largely aid the 
marine denudation on the sea-cliffs. 
The effects of ice are clearly traced by the presence of phe- 
nomena similar to those produced in countries where glaciers 
now exist. 
It must be remembered that the area now embraced by Eng- 
land has many a time been submerged beneath the ocean, and, 
indeed, the different rocks or strata of which it is composed are 
almost entirely, the consolidated ooze, mud, sand, and shingle of 
old sea-bottoms. These are our stratified rocks, and they have 
most of them (directly or indirectly) been formed by the de- 
struction of some pre-existing rocks, which formed the hills and 
the cliffs along the old sea-margin. Of what rocks the earliest 
hills and valleys were formed it is not easy to say, but they 
must all have belonged to the igneous class, and have been of 
a more or less crystalline nature. The history of the earth, as 
told by our stratified rocks, indicates an incessant change. No 
new materials are added (if we except the slight additions 
made by meteoric stones and dust), but all are ever undergoing 
some change either in form or in combination. 
From the greater portion of our rocks being deposits formed 
in the ocean, it might at first naturally be supposed that the 
sea, was the great agent of destruction. A few moments’ reflec- 
tion will, however, show how erroneous such a conclusion would 
be, for the greater part of the material worn from the land is 
carried out to sea by rivers, and there mingled with the marine 
shells and the sediment due to the waste of the sea-cliffs ; so 
that it would evidently be giving too much credit to the de- 
structive power of the sea, great as it is, to consider most of the 
matter deposited at its bottom as owing to its wear and tear. 
The earlier deposits having been upheaved and formed dry 
land, while other and newer deposits were being formed, and 
partly by their destruction, it follows that, during repeated ele- 
vation and submergence, the older rocks will have suffered more 
by denudation of all kinds than the newer. Moreover, they 
having been subjected to great pressure from superincumbent 
strata subsequently removed, and having been more altered or 
metamorphosed by contact with igneous rocks than the newer 
strata, their texture is or has been continually hardening, and 
therefore the older rocks as a rule are of a more stony or slaty 
nature than the newer, which in most cases have suffered little 
from volcanic or igneous action. 
