482 VAST AMOUNT OF SUBSIDENCE [chap. xx. 



oscillations of level ; we see in each barrier-reef a proof that die 

 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 Ju- 

 terchaiiged. 



