268 



Christmas Island. 



No. 658. A hard rock associated with chalk-like rock on plateau. 



Composition : Ca C O3 = 60-27, Mg C O3 = 39-57. Total = 99-84. 

 A crumbling, porous, white limestone. 



The slide consists almost entirely of idiomorphic zoned crystals 

 of dolomite. The irregular empty spaces and cracks which occur 

 are, however, usually bordered by clear crystals. Most of the 

 organisms have been obliterated, but one or two specimens of 

 Amplmtegina and possibly Polytrema occur. The dolomite 

 crystals usually have dark centres, from which small, dark, acute 

 crystals (? calcite) are projecting in some cases. In other places 

 organic fragments are recrystallizing in the form of these long 

 dark (? scalenohedral) crystals of (? calcite). 



No. 378. Highest rock collected from Murray Hill, at about 

 1,100 feet. 



Composition : Ca C O3 = 60-34, Mg C O3 = 40-02. Totals 100-36. 

 A cream-coloured, hard, compact rock. 



Irregular cavities and cracks occur, and both are filled, or 

 partially filled, with large clear rhombohedral crystals. A fair 

 amount of semi-opaque material remains irregularly distributed 

 over the slide. Very few of the rhombohedra are zoned, and most 

 are very small. A few organisms remain, especially a meandrine 

 form (? Polytrema), and some organic fragments are recrystallizing, 

 showing acute crystals of calcite (?) projecting at right angles to 

 the length of the fragment. 



No. 514. Near the summit over Flying Fish Cove, at 880 feet. 



Composition: Ca C 03= 59-33, Mg C 03 = 40-88. Total = lQQ-2\ . 

 A cream-coloured spongy limestone. 



Yery similar to No. 378, but the dolomite crystals are larger 

 and less semi-opaque material is present, but zoning is not well 

 seen. The only remaining organisms are meandrine forms 

 (? Polytrema) and fragments undergoing recrystallization. 



Analyses or Eock- Specimens from Cheistmas Island. 



Nuniher. 

 134 

 179 

 308 

 378 



514 I \^\ ^^""P}^ 

 ( 2nQ sample 



658 



800 



804 



811 



963 



