MINERALOGICAL CHANGES OBSERVED IN CORES OF FUNAFUTI BORINGS. 399 



This phenomenon is seen only when the organisms possess a well-marked crystalline 

 structure. When they do not, the product of crystallisation is usually an aggregate 

 of granular calcite, the elements of which rarely show any marked relation to those 

 of the contiguous organisms (figs. 33, 37). 



Fig. 32.— Main Boring. Core 105. Depth 90-100 Fig. 33.— Main Boring. Core 141. Depth 160 feet. 



feet. X 100. X 100. 



Coral showing fine calcareous detritus in process Fine interstitial calcareous detritus in process of 



of conversion into aragonite. conversion into calcite. Some of the calcite has 



^ also been contributed by deposition from solu- 

 tion. 



But although examples ol perfectly crystallised " mud" are frequently seen in the 

 sections, the actual proportion of it which undergoes complete clarification is quite 

 small. Much of it is found, even in the deepest parts of the boring, almost as fresh 

 in appearance as that which has been but recently deposited. In reality this has 

 undergone crystallisation, but the granular elements into which it has been transformed 

 are so exceedingly small that a casual inspection gives the impression that it is quite 

 unchanged. The crystallisation of the fine detritus in this imperfect manner is one 

 of the very first of the changes that take place in the rocks ; its more perfect 

 crystallisation must be regarded as somewhat exceptional. 



Before dismissing the subject of the fine detrital matter, it will be convenient to 

 mention here that it is not all contemporaneous — using that term in a broad sense — 

 with the rocks in which it occurs. Some of it, on the contrary, is of subsequent 

 origin, having made its way into the rocks after the lapse of a longer or shorter period 

 during which the cavities had become lined with crystals deposited from solution 

 (figs. 34, 46). Moreover, the cavities which arise in the rocks by the removal of 

 organisms in solution are frequently seen to contain fine calcareous material, which 

 must obviously be of comparatively late introduction into the mass (fig. 65). This, 



