610 



FOEMATION OF COEAL EEEFS. 



[Ch. XLIX. 



# 



much, carbonic acid^ and a small quantity of carbonate of 

 lime. But tliere is no marl in Loch Fithie, near Forfar, 

 Avhere there are no sjprings, although that lake is surrounded 

 by these calcareous deposits, and although, in every other. 



r 



accumulat 



testacea. 

 We fix 



im 



pregnated with carbonate of lime. We know that, if the 

 common hen be deprived altogether of calcareous nutriment, 

 the shells of her eggs will become of too slight a consistency 

 to protect the contents ; and some birds eat chalk greedily 

 during the breeding season. 



If, on the other hand, we turn to the phenomena of inor- 

 ganic nature, we observe that, in volcanic countries, there is 

 an enormous evolution of carbonic acid, either free, in a 



& 



mix 



districts are usually impregnated with carbonate of lime in 



one who has travelled in Tuscany, 



great abundance. 



No 



through the region of extinct volcanos and its confines, or who 

 has seen the map constructed by Targioni (1827), to show 



mineral 



ubmero'ed 



mig^ht suDnlv materials 



The importance of these springs is not to be estimated by the 

 magnitude of the rocks v/hich they have thrown down on the 

 slanting sides of hills, although of these alone large cities 

 might be built, nor by a coating of travertin that covers the 

 soil in some districts for miles in length. The greater part 

 of the calcareous matter passes down in a state of solution 

 to the sea, and in all countries the rivers which flow from 

 chalk and other marly and calcareous rocks carry down vast 

 quantities of lime into the ocean. Lime is also one of the 

 component parts of augite and other volcanic and hypogene 

 minerals, and when these decompose it is set free, and may 

 then find its way in a state of solution to the sea. 



The lime, therefore, contained g^enerally in sea-water, and 

 secreted so plentifully 



Pacific, may have been < 



the testacea and corals of the 

 ^ed either from springs rising up 



ii^ 



ii^ 



4 



(f 



