CH. xxvi. AQUEOUS ROCKS. 219 



they must compare these with the older rocks in the crust 

 of the earth, and see whether they were not formed in the 

 same way. 



Aqueous (or water-made) Rocks. When we find a 

 piece of marble made up almost entirely of oyster and other 

 shells, and of pieces of coral, we cannot doubt that it must 

 once have been a heap of loose shells and corals such as we 

 now see on the shore or under the water, and that it has since 

 been hardened into limestone. When we find that by 

 crushing or scraping sandstone we can turn it into sand like 

 that which we see on the seashore, and which we know has 

 been made by the sea grinding the stones and rocks of the 

 beach against each other, then we cannot doubt that the 

 sandstone has once been loose sand, and before that was 

 part of a rock which has been ground down by the waves. 



And so we are led to the conclusion that the rocks of 

 our earth, as we see them now, have been formed out of the 

 materials of still older rocks which existed before them, and 

 are being .gradually moulded into other and newer rocks, 

 which will exist when these have been destroyed. Our solid 

 earth is being wasted every day. The sides of the moun- 

 tains are washed down and their materials are carried through 

 the valleys by the running water. In this way the soil is 

 brought down to the coast, and here it is eaten away by the 

 waves of the sea, and falls to the bottom of the ocean, out 

 of which it will be raised again by earthquakes, volcanoes, 

 and other movements of the earth's crust, such as can be 

 proved to be going on in parts of the world at this day. As 

 far back as investigations and reasoning can go we find 

 everywhere signs that these gradual and incessant changes 

 have always been going on, and that the face of our earth, 

 as we now see it, has been moulded out of the ruins of an 

 older world. 



