482 H. S. JEVONS, H. I. JENSEN, T. G. TAYLOR AND C. A. SUSSMILCH. 



The plagioclase possesses the extinction angles of labra- 

 dorite. The mean refractive index of most of the felspar 

 is 1*558, but there is some as low as 1*540, and some that 

 is intermediate between these figures. Probably we have 

 mainly labradorite surrounded by andesine and a small 

 amount of oligoclase, which in places approaches albite. 

 The felspar does not gelatinise with acid (HC1). It is 

 largely decomposed and replaced by chlorite, sericite, 

 kaolin, analcite, and zeolites. 



The ilmenite is idiomorphic, presenting hexagonal and 

 lath-shaped sections. As noted above it is attracted by a 

 magnetite intergrown with it. This is also confirmed by 

 the result of the bulk-analysis of the rock which shows a 

 comparatively small amount of Ti0 2 . 



Of the decomposition products augite has given rise to 

 chloritoid, some of which is closely allied to ottrelite and 

 to chlorite, probably chlinochlore. Most of the serpentine 

 is after olivine, but some of it seems to replace augite — if 

 it was not derived from it. The analcite occurs chiefly in 

 large irregularly rounded masses enclosing crystals of the 

 ferro-magnesian minerals and apatite. It also occurs in 

 angular interstitial masses, some of which do not contain 

 apatite. This is easily accounted for however on the 

 supposition of secondary derivation from felspar, by the fact 

 that much of the felspar does not contain apatite. It is 

 significant that the comparison of a number of specimens 

 shows that the quantity of analcite in both of these forms 

 increases pari passu with the state of decomposition of 

 the rock. 



Order of Consolidation. 



Olivine 



Ilmenite 



Biotite 



Apatite 



Augite 



Plagioclase 



