508 CHARLES DARWIN 



reared and preserved wonderful memorials of the subter- 

 ranean oscillations of level; we see in each barrier-reef a 

 proof that the land has there subsided, and in each atoll a 

 monument over an island now lost. We may thus, like unto 

 a geologist who had lived his ten thousand years and kept a 

 record of the passing changes, gain some insight into the 

 great system by which the surface of this globe has been 

 broken up, and land and water interchanged. 



