180 



W. N. BENSON. 



ites, the theralites and the basanites. The most remark- 

 able rocks are the theralites (Nos. 3 and 4 of Mr. Wilkinson's 

 figure) that occur on the slopes of Barrington Trig. These 

 two rocks differ only in grain size and amount of zeolite 

 developed. They are very coarsely granular with exceed- 

 ingly well marked zonary structure in their deep purple 

 augites. The predominant salic mineral is a labradorite in 

 tabular crystals, and there are also large crystals of ilmenite 

 and prisms of apatite. In addition to this, there is a certain 

 amount of clear nepheline. All these different minerals 

 can readily be distinguished with the naked eye in the slide 

 of No. 4, of which Plate 6, fig. 1 is a photograph. In 

 addition, there is a small amount of zeolite developed by 

 alteration of the nepheline. 



The most interesting feature, perhaps, is the occurrence 

 of a second generation of augite of a more greenish tint 

 than that of the phenocrysts, and this forms a granophyric 

 intergrowth with the nepheline, either in little hooked-like 

 pieces fig. 3 (a), or in peculiar arrow-head shapes fig. 3 (b). 1 



Fig. 3. Graphic inter- 

 growths of augite shaded, 

 and nepheline clear, in 

 theralite. 



(a) from Stewart's 

 Brook, magnified 80 

 diameters. 



(b) from Barrington 



Trigonometrical Station 



hill, magnified 22 diam. 



This is an enlarged draw- 

 ing of the large nepheline 

 grain visible in the centre of 

 fig. 1, Plate 6. 



1 Cf. Fig. 

 p. 271. 



B, A. Harker, The Natural History of Igneous Rocks, 



