SOURCES OF LIME IN CORAL. 515 



tity of lime deposited by them ; and this question affects not 

 only those of the present epoch, but those of former ages, to whose 

 labours, in conjunction with those of the testaceous Mollusks, the 

 greater part of the Calcareous strata of the secondary and sub- 

 sequent periods are immediately or remotely due. Some have gone 

 so far as to imagine, that the lime is produced by some organic pro- 

 cess in the animals themselves. No positive evidence of such a 

 production can, however, be obtained from any source ; and the 

 hypothesis is quite unnecessary in the present instance. We 

 have reason to believe that lime existed in large quantities on 

 the surface of the earth, before any organised beings were placed 

 upon it ; and there is also ground for supposing, that a larger 

 quantity of carbonic acid existed in a free state at that epoch, 

 than at the present time. It is not improbable, therefore, that 

 the waters of the ocean contained a much larger quantity of lime 

 than they now do this ingredient being held in solution by the 

 free carbonic acid ; and the enormous beds of calcareous rock, 

 separated by the action of Coral-polypes, are therefore easily 

 accounted for. Moreover, in volcanic countries at the present 

 time, springs charged with carbonate of lime thus held in solution 

 are very abundant ; and it is not unfair to suppose that, as the 

 part of the globe in which the coral-formations increase most 

 rapidly (the Pacific Ocean), is also one of the chief areas of 

 submarine volcanic action, such springs may occur with similar 

 frequency, and may greatly assist in the growth of these masses. 

 In illustration of this doctrine, it is remarked by Mr. Lyell that, 

 in lakes which have no unusual supply of carbonate of lime, 

 there is no accumulation of shell-marl the thin shells of one 

 generation of Mollusks decomposing, so that their elements supply 

 the requisite materials to succeeding races. But, if springs or 

 streams charged with carbonate of lime enter such a lake, the 

 shells accumulate and form marl. There are many plants and 

 animals, in whose economy lime appears to be an important agent; 

 and the quantity introduced bears a strict relation (within a 

 certain limit) to that with which they are supplied. 



