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Transactions. 



ters : In the centre is the rounded core of horneblende, evidently 

 from its pleochroic characters rich in iron. This is surrounded 

 by a granular mass of opaque small rounded grains. Some of 

 these grains are yellow in reflected light and others black, thus 

 showing themselves to be pyrites and magnetite. They occur 

 in about equal proportions. Between these grains small plates 

 of green aegerine are to be seen, and needles and basal sections 

 of clear apatite showing the typical uniaxial characters of that 

 mineral. In places small pieces of the hornblende also occur 

 interstitially. There is, besides, an isotiopic mineral whose 

 characters show it to be analcite. It is a decomposition pro- 

 duct such as would be expected in an alkaline rock. 



These granular masses with their central core of hornblende 

 form an interesting example of resorption zones. They are in 

 no way the result of weathering, but result from the chemical 

 effect of either the magma or superheated percolating solutions. 

 The original hornblende has been acted upon by one of these 

 agencies, with the resulting granular mass of eegerine, pyrites, 

 and magnetite. Where no core of the hornblende remains 

 the mass has a distinct hornblendic habit as a whole, being 

 cither a rounded mass such as would result from the cutting 

 of an irregular crystal of hornblende parallel to the base, or else 

 showing as a prism. Where interstitial hornblende remains, or 

 where a core is left, its orientation is the same as that of the 

 mass surrounding it. The apatite needles were originally in 

 the hornblende, a feature very common in this mineral. The 

 order of consolidation has been (1) apatite, (2) hornblende, 

 (3) nepheline, (4) feldspar, (5) resorption action and consolida- 

 tion of pyrites in the body of the rock. 



Decomposition of the feldspars has produced kaolin and not 

 serecite. 



A chemical analysis of the rock gave as follows : — 



Per Cent. 

 SiOo •• •• •• •• 50-8 



A1,0 3 



Fe,0 3 



CaO 



MgO 



K 7 



Na,0 



22-5 

 91 

 2-3 

 1-4 

 39 

 5-7 



99-6 



Prom a comparison of this analysis with those given by 

 Rosenbusch* the rock most closely resembles an amphibole 



I '.Mil. 



* " Elemente der Gesteinslehre " (ref. p. 131, Analysis, p. 29, No 10). 



