Thomson. — Rocks from Parapara, Bluff Hill, and Waikawa. 39 



The feldspars are often rounded, and show good albite twinning with rarer 

 pericline lamellse. The extinction angles are characteristic of basic labra- 

 dorite. Of the secondary minerals the chief is tremolite, oriented in crystal- 

 lographic continuity with its host. This structure, described by me* in the 

 amphibolite of Glendalough, Ireland, is commonly ascribed to the uralitisa- 

 tion of pyroxene, but may also arise, as shown at Glendalough, from the 

 amphibolitisation of olivine. Probably both methods have operated here. 

 Occasionally small fibres of tremolite oriented independently of the host 

 occur in these areas. The feldspar inclusions are sometimes wholly or 

 partly replaced by clinozoisite associated with muscovite and a feebly bi- 

 refringent chlorite. The green margins of the hornblende plates contain 

 similar inclusions, and, in one case, twinned clinochlore and small prisms of 

 pale actinolite. 



Only one large crystal of biotite is seen in the section, and it includes 

 hornblende. 



Outside the large pcecilitic plates, feldspars altering to clinozoisite and 

 muscovite are not rare, but there is a large development of recrystallized 

 actinolitic hornblende fibres pointing in all directions, but most often distinctly 

 aggregated in bundles, and interspaced with most of the secondary minerals 

 included in the large plates. There are, in addition, some areas consisting 

 of finely divided talc, into which fibres of hornblende project. It is difficult 

 to be sure of talc in the presence of sericitic muscovite, since there is no certain 

 microscopic method of discriminating between these minerals, unless recourse 

 be had to microchemical tests ; but the mineralogical association supports 

 the general appearance. These areas do not contain clinozoisite or epidote, 

 which are associated with muscovite in the altered feldspars, and contain 

 hornblende, which does not occur in the latter. Assuming the presence of 

 talc, these areas are then pilitef after olivine, and the rock is derived from 

 a hornblende olivine dolerite such as Harkerf describes from Anglesey in 

 association with hornblende-peridotites. 



* Thomson, J. A. "The Homblendic Rocks of Glendalough and Greystones." 

 Q.J.G.S., Ixiv, p. 475. 1908. 



f Becke, F. " Eruptiogesteine aus der Gneissformation des niederosterreichischen 

 Waldviertels." Isch. min. u. petr., Jlitt. v, p. 147. 1883. 



J Harker, A. " The Bala Igneous Rocks of Carnarvonshire," pj). 92, 97. 



