1397] DISTRIBUTION OF PELAGIC FORAMINIFERA 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.! JOHN Murray. 
1 See Murray and Irvine, op. cit., table on p. 106. 
