174 F. L. StiUiceU: 



chloride and logwood are applied to the surface of the slice, 

 and allowed to stand for a few minutes. The dolomite is 

 unaffected, but over the calcite a gelatinous precipitate of 

 aluminium hydrate is formed, and this is stained purple with the 

 logTA^ood. The section is then mounted in glycerine jelly. No 

 decided differentiation resulted with the impure rock from D; 

 but the rock from C gave very interesting results. 



Petrogi-apliical Characters. 



Specimen No. 38, collected from C, Section X., Will Will 

 Rook. Megascopically this is a very hard, fine-grained, greyish 

 and earthy limestone. It is slightly cavernous, and the caverns 

 appear to be lined with more crystalline material. Scattered 

 throughout are small crystals of quartz and occasional felspar 

 and fragments of igneous material. 



Microscopically the bulk of the rock is a crypto-crystalline 

 mass of earthy carbonate in which are set angular and sub- 

 angular crystals of quartz and occasional felspar. Isolated 

 lumps of igneous material contain lumps of plagioclase felspar 

 and grains of olivine set in a brownish glass, thus indicating 

 basaltic material. Along the cracks and caverns in the slice 

 crystallisation has occurred, and this has been well brought 

 out by the staining. The crystallised material is for the most 

 part purple, and therefore calcite in very minute crystals. But 

 in many of the cavities, most pronounced in those completely 

 filled with crystalline material, only the inner part consists of 

 calcite, between which and the wall of the cavity is a ring of 

 unstained dolomite, which is well defined from the ground-mass. 



The rock may therefore be described as a dolomitic limestone. 

 Specimen No. 39, collected from D, is, megascopically, rather a 

 loosely compacted, whitish rock, which* contains numerous 

 pebbles of rounded and sub-angular quartz, felspar and basaltic 

 material, set in a white calcareous material. The pebbles are 

 very loosely set, and readily torn out on slicing. 



Microscopically, it is seen to consist very largely of quartz 

 pebbles, lumps of basalt, and felspar set in an exceedingly fine- 

 grained ground-mass of calcareous material. Re-crystallisation 

 has not proceeded at all, and very little was gained by staining. 



The rock may be described as a detrital limestone. 



