414 



DR. C, GILBERT CULLIS. 



crystals which may have been in part deposited directly as such, or may represent 

 secondary calcite dolomitised ; a portion of the fibrous encrusting material also is 

 generally composed of dolomite ; and when finely divided detritus occurs, it, too, is 

 dolomitic almost without exception. Higher up and lower down the secondary calcite 

 more or less completely disappears, being gradually replaced by dolomite ; and, 

 lastly, the calcite organisms are afiected ; some alter earlier than others, but prac- 

 tically all have suffered conversion into dolomite when the upper limit of 1050 feet, 



Fig. 48.— Main Boring. Ccne G7lA. Depth 

 1090 feet, x 200. 



Partially dolomitic encrusting deposit occupying 

 a cavity in dolomitised coral. The recrystal- 

 lised coral substance is separated from the 

 filirous material by a layer of comparatively 

 clear dolomite crystals. Of the five layers of 

 the encrusting deposit the first, third, and fifth 

 are of calcite, the second and fourth of dolo- 

 mite. 



Fig. 49. 



-Main Boring. 

 1114 feet. 



Core 709a. 

 X 35. 



Depth 



Section of the deepest core. The organisms are 

 bound together by a cement of three layers. 

 The first layer is fibrous and somewhat opaque 

 with included " mud " ; the second layer is a 

 little more definitely crystallised and is less 

 opaque with included matter ; the third layer is 

 well ciystallised and water-clear. Organisms 

 and cement alike are composed of dolomite. 



or the lower limit of 1070 feet, is reached. None of the rocks included in this 

 20 feet show signs of solution. 



c. The Characters of the Lowest Rocks reached in the Bormrjs. 



From 1070 feet to the bottom of the boring (1114 feet) the rocks consist once more 

 of dolomite, to the complete or almost complete exclusion of visible and recognisable 

 calcite. What little calcite they do occasionally contain consists, for the most ])art, 

 of undolomitised or incompletely dolomitised calcite organisms ; occasionally also the 



