BY W. G. WOOLNOUOH. 801 



siderable quantity of the mineral was isolated, and analysed by 

 Mr, A. B. Walkom with the following result : — 



SiOg 50-71 



AI2O3 2-07 



FegO,, 0-69 



MgO 007 



CaO 46"53 



Total 100-07 



There can be little doubt, then, that the mineral is wollastonite; 

 but I can suggest no explanation for the slightly oblique extinc- 

 tion-angle above noted. Inclusions in the wollastonite are very 

 abundant in the form of relatively large rounded grains of 

 vesuvianite. 



It is possible that there is a second pyroxenic mineral like 

 malacolite present in small quantities; but, if so, its distinction 

 from the wollastonite is very difficult. Certain grains appear to 

 be too strongly birefringent to be classed as wollastonite, and 

 possess the cleavage of malacolite, )>ut in no case could an 

 optically positive figure be obtained. 



A little colourless and slightly decomposed scapolite is present 

 in the form of ovoid grains. 



The groundmassof the rock is a greyish-yellow laminated mass 

 of mineral, with an internal parallel fibrous structure. The 

 fibres are at right angles to the laminae, which are constant in 

 direction throughout the whole slide. This mineral is not per- 

 fectly isotropic; in thick sections it is faintly birefringent, butthe 

 double refraction is even lower than that of vesuvianite. It is 

 probable that this material is incipient garnet, since, in speci- 

 mens a little closer to the granite-boundary, garnet becomes the 

 most abundant mineral. Even in this rock there is a little light 

 yellow garnet intergrown with the vesuvianite, as above noted. 



There is a small amount of yellowish phlogopite-mica in 

 rounded flakes, and considerable interstitial calcite. 

 82 



