Ic^ 



■-■(s. 



'H to 



\ 





in 



k 



?^ 



re 



are 



tor 



Ho 



We 



are 



^^^1 StTQ, 



lO 



*<rf» 



T 



^^) in tie 



bribed b 

 exliibitini 



^? ^e mar ■ 



ar, tie 



^ intlie 

 he grouna 



prfiicli ::^^ 



le smice, 

 he marp 



• eiamples 

 above tk 



} instance 



iritiiis, ife 



to be 



or 



ajs, 



barrier 



Jlr be ^^■ 



ftbe 



«I 



>on 



atoll 



piO 



^aD^ 



. .n.^i^^' 



id^ 



Jiir 



4. 



lao 



im 



to 



Ch xlix.] the theoey of subsidence consideeed. 



G07 



ill futurity as tlie secondary rocks are in tlie past, 



the bed of 

 the Pacific with its atolls and barrier reefs should be con- 

 verted into a continent, we may conceive that scarcely any 

 or none of the existing reefs would be preserved, but only 

 widely spread strata of calcareous matter derived from their 



wear and tear.'^ 



When it is nrged in support of the objection before stated 

 (p. 603) that the theory of atolls by subsidence implies the 

 accumulation of calcareous formations 2,000 or 3,000 feet 

 thick it must be conceded that this estimate of the min- 

 imum density of the deposits is by no means exaggerated. 

 On the contrary, when we consider that the space over which 



atoll 



3 



may 



be compared to the whole continent of Asia, we cannot 

 but infer from analogy that the differences in level in so 

 vast an area have amounted, antecedently to subsidence, to 

 5,000 or even a greater number of feet. Whatever was the 

 difference in height between the loftiest and lowest of the 

 original mountains or mountainous 



islands on which the 



must 



them 



level. Flmders, therefore, by no means exaggerated the 

 volume of the limestone, which he conceived to have been 

 the work of coral animals ; he was 



he was merely mistaken as to 

 the manner in which they were enabled to build reefs in an 



unfathomed ocean. 



But is it reasonable to expect, after the waste caused by 

 denudation, that calcareous masses, gradually upheaved in an 

 open sea, should retain such vast thicknesses ? Or may not 

 limestones of the cretaceous and oolitic epochs, which attain 

 in the Alps and Pyrenees a density of 3,000 or 4,000 feet, and 

 are in P-reat nart made ud of coralline and shelly matter. 



present us with a true geological counterpart of the recent 



coral reefs of equatorial seas ? 



emm 



r. 



Miocene 



of Jamaica are 



enormously thick. 



Before we attach serious importance to arguments founded 



* Letter to Mr. Maclaren, Scotsman, 18-13 



