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Ch. XLIX.] 



ME. DAEWIN'S MAP OF CORAL EEEFS. 



G03 



northern point of Australia, placed on tlie borders of an area 

 of subsidence ; but it lias been since proved tliat tliis volcano 



J 



lias no existence. 



We see^ therefore^ an evident connection^ first^ between tlie 

 burstino- forth every now and then of volcanic matter through 

 rents and fissures^ and the expansion or forcing outwards of 

 the earth's crusty and^ secondly, between a dormant and less 

 enero-etic development of subterranean heat, and an amount 

 of subsidence sufficiently great to cause mountains to dis- 

 appear over the broad face of the ocean, leaving only small 

 and scattered lagoon islands, or group of atolls, to indicate 

 the spots where those mountains once stood. 



On a review of the differently-coloured reefs on the map 

 alluded to, it will be seen that there are large spaces in 

 which upheaval, and others in which depression prevails^ 

 and these are placed alternately, while there are a few 

 smaller areas ivhere movements of oscillation occur. Thus 

 if we commence with the western shores of South America, 

 between the summit of the Andes and the Pacific (a region 

 of earthquakes and active volcanos), we find signs of recent 

 elevation, not a^ttested by coral formations, which are want- 

 ing there, but by upraised banks of marine shells. Then 

 proceeding westward, we traverse a deep ocean without 

 islands, until we come to a band of atolls and encircled 

 islands, including the Dangerous and Society archipelagos, 

 and constituting an area of subsidence more than 4,000 miles 

 long and 600 broad. Still farther, in the 

 reach the chain of islands to which the New Hebrides, 

 Salomon, and New Ireland belong, where fringing reefs and 

 masses of elevated coral indicate another area of upheaval. 



same 



New Hebrides we meet 



New 



barrier, implying a second area of subsidence. 



The only objection deserving attention which has hitherto 

 been advanced against the theory of atolls, as before ex- 



Mr. Maclaren 



On the 



outside,' he observes, ' of coral reefs very highly inclined, no 



* Scotsman, Nov. 1812, anclJameson's Edin. Journ. of Science, 1843. 



