420 



Transactions. 



Muscovite is present in small amount with the biotite, and epidote is very 

 plentiful and moderately coarse. Sphene is abundant in coarse character- 

 istic wedge-shaped crystals. Magnetite occurs sparingly in coarse crystals, 

 and apatite and zircon are accessories. 



The chief interest lies in the epidote. This is a pleochroic pale-yellow 

 to colourless variety, with the usual optical characters. It is very frequently 

 enclosed as sharply euhedral crystals in feldspar; sometimes nests of sharply 

 bordered rounded grains are enclosed pseudo-poecilitically by the feldspar. 

 Very commonly it is enwrapped or enclosed, sometimes as idiomorphic 

 crystals, by the brown biotite. This last mineral is thus important in its 

 relations to the epidote ; there can be little doubt that it is primary : all 

 indications point to this conclusion. 



Representation of the relations of epidote to hornblende, plagioclase, 

 and biotite in a granodiorite from Reefton. Crossed nicols. 

 X 60 approx. Qu = quartz ; PI = plagioclase ; Bi = biotite ; 

 Ej> = epidote ; Ap = apatite ; Ho = hornblende ; Mi = micro- 

 cline. 



An important fact bearing on the question of the primary character of 

 the epidote is that, in no less than seven cases in the two sections cut of the 

 rock under consideration, the mineral surrounds a central crystal of brown 

 hornblende ; only one or two hornblende crystals were observed that were 

 not in association with the epidote. In all cases the amphibole is in small 

 crystals. 



At first thought the above facts would suggest that the epidote is an 

 alteration product of the amphibole ; but against this view it is to be observed 

 that the idiomorphic epidote enclosed in feldspar or biotite does not present 

 the outlines of hornblende crystals. Possibly some of the epidote has been 

 derived thus, but it appears more probable that the epidote, in great part 



