1897 j DISTRIBUTION OF PELAGIC FOEAMINIFERA 27 



quickly soluble than the calcite form in the proportion of about three 

 to two. Both aragonite and calcite are apparently very partially 

 soluble in sea-water which does not contain free or loosely-combined 

 carbonic acid, but when these dead shells are in contact with decaying 

 organic matter, giving off carbonic acid, they are rapidly dissolved. 

 An experiment with Globigerina Ooze in a sea- water containing 

 additional carbonic acid showed that the thin walls of the chambers 

 of the shells were first dissolved, leaving rings of the thicker por- 

 tions of the Pulvinulina shells, for example. Decaying organic 

 matter has a powerful solvent action on carbonate of lime, due to 

 two causes : (1) by the carbonic acid formed as one of the products 

 of this decay, and (2) on account of the formation of sulphides and 

 sulphuretted hydrogen, due to the reduction of the sulphides present 

 in sea-water. 1 John Murray. 



1 See Murray and Irvine, op. cit., table on p. 106. 



