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C. A. SUSSMILCH AND W. G. STONE. 



of a ferro-magnesian mineral. It is sparingly scattered 

 through the groundmass. A little of it appears to be 

 leucoxene, but generally it is impossible to distinguish 

 between the magnetite and ilmenite. A few specks of iron 

 pyrites were detected with aid of lens in hand specimens. 



Apatite occurs sparingly as small crystals in the chlorite 

 patches and groundmass. It is included also occasionally 

 as needle-like crystals in the felspars. 



The secondary minerals are chlorite, calcite, epidote, 

 kaolin, and a sericite-like material. 



Chlorite is very plentiful and occurs in patches of a light 

 green colour up to 2 or 3 mm. in size. The average size is 

 about 1 mm. It is slightly pleochroic, shows very low 

 interference colours, and is sometimes practically isotropic. 

 It is probably the variety pennine. It undoubtedly repre- 

 sents, in a large part, the alteration of a ferro-magnesian 

 mineral, and is often associated in this connection with 

 calcite and iron ores. It also probably represents complete 

 pseudomorphs after felspar as these show various stages of 

 alteration. Chlorite, also of a fibrous nature, constitutes 

 in large part the groundmass, giving to it the prevailing 

 brownish-green to green colour. In most sections examined 

 the matrix has been largely chioritised, in some completely 

 so. 



Calcite is fairly plentiful and would reach in quantity 

 that indicated by the analysis, about 4%. It occurs some- 

 times in patches up to 3 mm. showing typical cleavage. 

 Some of it no doubt is entirely secondary, i.e., been intro- 

 duced wholly into the rock by the action of percolating 

 water, but the main bulk is probably due to the alteration 

 in situ of lime bearing minerals by the action of percolating 

 solutions containing carbonic acid. It is an alteration 

 product of the felspar, ferro-magnesian mineral, and ground- 

 mass. The felspar shows various stages of alteration and 



