48 ANNUAL ADDRESS, MDCCCLXXIII. 



lake of Constance containing 30 per cent, of carbonate of lime. 



Bischoff himself in another part of his great work on 

 Chemical Geology writes, " In the sea, and especially on 

 the coasts, the condition for the deposition of carbonate 

 of lime exists, and there the agitation of lime in the 

 water exists to the greatest extent, that is, in allowing 

 carbonic acid to get more intimately mixed with sea 

 water, and so to precipitate chemically the carbonate of 

 lime." This statement appears to me to be at variance 

 with what I have quoted from the same author on the 

 previous page. 



The following extracts from Mr. Sterry Hunt's work 

 on the chemical and mineralogical relations of metamorphic 

 rocks, with which I was unacquainted when I wrote this 

 address, and which have been since pointed out to me 

 by Mr. J. Plant, of Manchester, will help to show there 

 are weighty reasons for doubting the theory of the or- 

 ganic origin of limestone. 



He writes, " It cannot be doubted that in the earlier 

 periods of the world's history chemical forces of certain 

 kinds were much more active than at the present time. 

 Thus, the decomposition of earthy and alkaline silicates, 

 under the combined influence of water and carbonic acid, 

 would be greater when this acid gas was more abundant 

 in the atmosphere and the temperature probably higher. 

 The large amounts of alkaline and earthy carbonates then 

 carried to the sea from the decomposition of these silicates 

 would furnish a greater amount of calcareous matter to 

 the sediments." 



The sources of the carbonates of lime and magnesia in 



