BY W. N. BENSON. 527 



Besides the locality mentioned above, it occurs in Portion 5. 

 Here the rock is less decomposed, and the fibres are not separable. 



iii. — The Granites, Granophyres, and Aplites. 



The main mass of the granite in this district lies in the north- 

 eastern portion of the Parish of Galbraith, and north and north- 

 western portions of the Parish of Lowry, though its boundaries in 

 the latter Parish have not yet been mapped. In the preparation 

 of this paper, little work was done on the granites of the main 

 mass; and the rocks here described are almost entirely from the 

 innumerable granitic veins that intrude the slate. Before pass- 

 ing to their particular description, I may remark that the granites 

 of the main mass are much decomposed, and show few good 

 outcrops except at or near their junction with the slates. They 

 appear to be much intersected by aplite veins, which, decomposing, 

 are very like red sandstone in appearance. I learn from Mr. T. 

 C. Dwyer, B.Sc, that around Wimbledon, to the extreme north- 

 east of Galbraith, coarse pegmatite is abundant. Near the 

 boundary of the massif basic segregations are very common; the 

 rock in which they are situated is generally a fairly coarse-grained 

 (2-4 mm.) hornblende granite, with large orthoclase phenocr^'sts. 

 The segregations are usually spheroidal. A particular descrip- 

 tion of one is as under : — 



Macroscopical. — Fine-grained, dark blue granite. 



Microscopical. — Hypidiomorphic granular, with predominate 

 oligociase, and subordinate microcline, orthoclase, and quartz 

 Small phenocrysts of these last three occur, and larger ones of 

 oligociase. The coloured minerals are hornblende, green and 

 twinned, with brown biotite much less abundant. Magnetite 

 also is present. Sphene occurs in brown, pleochroic crystals, 

 passing into leucoxene. Apatite needles are frequent. 



Coming now to the granitic veins, these seem to run in a 

 general north and south direction, but branch a good deal. Two 

 of these (the westernmost that cross the railway) were traced as 

 far as possible, as shown on the map (Plate xxii.). They did not 

 pass either into pegmatites or quartz veins. Curran gives sketches 

 41 



