﻿480 



ME. J. A. THOMSON ON THE HOENBIEISTDIC [!NoV. 1908, 



enclosed in green hornblende, with a small intervening zone of 

 tremolite. Occasionally, instead of this massive replacement of 

 olivine, that mineral is replaced by a tangled aggregate of extremely 

 fine tremolite-needles (pilite of Prof. Becke). Talc, if present, 

 occurs in extremely small quantity. 



In some of these intermediate types, while there is no longer any 

 unaltered olivine to be seen, augite is abundant and mica appears. 

 It is feebly pleochroic, with strong birefringence and a low axial 

 angle. Its resemblance to that in the Schriesheim rock and that 

 in scheelite is very great. It forms plates which take their shapes 



Fig. 2. — Amphiholite from Glendalough, retaining the jpoecilitic 

 structure of tremolite within hrown Jiornblende. (Magnified 

 30 diameters.) 



from the small hornblende-prisms around, and seems therefore to be 

 of later formation and probably secondary. The plates are 

 frequently penetrated by flakes of tremolite, and with them 

 is associated occasionally a honey-coloured epidote in rounded 

 granules. The mica is clearly in course of alteration to the chlorite 

 above described (p. 479). 



(2) The AmpMbolite (fig. 3, p. 481). 



This type differs from the foregoing, in that the larger hornblende- 

 crystals are separated one from the other by a finer-grained material 

 of a lighter green, which is still formed mainly of hornblende but 

 in smaller crystals. Specific gravity = 3*04. 



