796 A TREATISE ON METAMORPHISM. 



substitution are fully considered below, in treating of "Recrystallization" 

 and " Dolomitization." The amount and speed of the recrystallization 

 depend, of course, upon many factors. Rather ancient limestones may 

 have been only partially recrystallized. On the other hand, the limestones 

 now forming may locally be coarsely crystalline. 



Commonly the mechanical and chemical forces work together in the 

 rearrangement of the rock. This is finely illustrated among the lagoons of 

 Florida and Australia. In these regions abundant life is building up calcium- 

 carbonate deposits. The deposits are being broken up by the waves; they 

 are being taken into solution by the sea; evaporation is going on; and 

 redeposition is occurring within the deposits. Thus in these regions, while 

 the first precipitation takes place as a consequence of the action of the 

 animals, the mechanical and chemical forces immediately begin to rearrange 

 the calcium carbonate into a detrital rock cemented by calcite, or into 

 coarsely crystalline rocks entirely dissolved and redeposited by means of 

 the chemical forces, or into a combination of these. 



Saville-Kent describes the main mass of the material upon which the 

 Australian corals are at present building their deposits as limestone con- 

 glomerates, largely built up of the cemented debris of corals and mollusks." 

 Tl. IV, A.) The breaking of the Barrier Reef is due to the waves; the 

 cementing of the material he attributes to evaporation during the low tide, 

 when the surface is above water, at which times the sun evaporates a large 

 amount of the interstitial water, and thus deposits material. It may be 

 supposed that this process is continuous, material being added to the solu- 

 tions at each time of high water and deposited at each time of low water. 

 But it may be doubted whether it is necessary for the reefs to be exposed 

 in order that consolidation shall occur. It seems highly probable that in 

 the ocean menstruum the limestone debris are consolidated by the chemical 

 processes of solution and deposition, even if the material remains continually 

 below the surface of the water. 



The process of recrystallization does not cease when the limestone 

 formations are raised above the sea. When these formations constitute 

 land, recrystallization continues under both mass-static and mass-mechanical 

 conditions. This is accomplished by the action of the underground waters 

 It has been fully explained that in its movement water is continually taking 

 material into solution and is continually depositing material from solution. 



« Saville-Kent, AV., The Great Barrier Beef of Australia, London, 1893, pp. 52-54. 



