402 



DE. C. GILBERT CULLIS. 



resulting from the reciystallisation of the aragonite of the cavities, is that the former 

 is less transparent than the latter, and still retains something of the yellowish or 

 brownish tint, which is so pronounced in sections of fresh coral, whereas the latter 

 is perfectly colourless (figs. 38, 57, 58). Ultimately, though at a lower level, even 

 this diiference disappears, and it is then often quite impossible to say of a mass that is 

 evidently altered coral, which part is altered coral substance, and which the crystallised 

 contents of the cavities. 



Fortunately a very considerable proportion of the organisms which have undergone 



!Fig. 37.— Main Boring. Core 145. Depth 170- 

 180 feet. X 100. 



Coral showing various stages in the conversion of 

 aragonite into calcite. The least altered part of 

 the coral is a fragment occurring embedded in 

 dense " mud " in the left lower quadrant of the 

 field ; the most altered occurs in the right lower 

 quadrant, where it has been completely con- 

 verted into graiuxlar calcite. The calcite of the 

 cavities is clearer than that of the coral sub- 

 stance. Two of the cavities contain " mud," 

 which has in one case been partially converted 

 into crystalline aragonite, and in the other into 

 crystalline calcite. 



Fig. 38.— Main Boring. Core 305. Depth 603- 

 612 feet, x 100. 



Coral completely converted into calcite. The 

 calcite of the ca\'ities is water-clear, that of the 

 coral substance somewhat opaque. 



recrystallisation, whether they be corals or not, are seen in section to be bounded 

 peripherally by a narrow dark band or line, which defines their original form and thus 

 causes their general outline to be still discernible (figs. G2, 63, 64, 68, 69). This dark 

 line probably results from the ])resence, upon the surface of the original organisms and 

 fragments, of a thin film of finely-divided detritus, which has not crystallised, or has 



