282 CORALS AND CORAL LSLANDS. 



show that they have undergone ; for since the Tertiary began 

 (or the preceding period, the Cretaceous, closed) more than 

 10,000 feet have been added to the Rocky Mountains, and 

 parts of the Andes, Alps, and Himalayas. 



Between the New Hedrides and Australia the reefs and 

 islands mark out another area of depression, which may have 

 been simultaneously in progress. The long reef of one hun- 

 dred and fifty miles from the north cape of New Caledonia, 

 and the wide barrier on the west, cannot be explained without 

 supposing a subsidence of one or two thousand feet at the 

 least. The distant barrier of Australia is proof of great sub- 

 sidence, even along the border of that continent. But the 

 greatest amount of sinking took place, in all probability, over 

 the intermediate sea, called the " Coral Sea," where there are 

 now a considerable number of atolls. 



HI. EFFECT OF THE SUBSIDENCE. 



The facts surveyed give us a long insight into the past, and 

 exhibit to us the Pacific once scattered over with lofty lands, 

 where now there are only humble monumental atolls. Had 

 there been no growing coral, the whole would have passed 

 without a record. These permanent registers exhibit in en- 

 during characters some of the oscillations which the " stable " 

 earth has since undergone. 



From the actual size of the coral reefs and islands, we know 

 that the whole amount of high land lost to the Pacific by the 

 subsidence was at the very least fifty thousand square miles. 

 But since atolls are necessarily smaller than the land they 

 cover, and the more so, the further subsidence has proceeded ; 

 since many lands, owing to their abrupt shores, or to volcanic 

 agency, must have had no reefs about them, and have dis- 

 appeared without a mark ; and since others may have subsided 

 too rapidly for the corals to retain themselves at the surface ; 

 it is obvious that this estimate is far below the truth. It is 

 apparent that, in many cases, islands now disjoined have been 

 once connected, and thus several atolls may have been made 



