236 



From this he is led to suggest that 'the gabbro-grano- 

 phyre melange rocks owe their origin to the interaction of 

 a normal basalt magma with a highly siliceous country rock, 

 in the manner advocated by Dr. Daly, and that the normal 

 granophyric-diabases, with their remai'kably constant chemi- 

 cal composition, represent the saturation point of such a 

 magma with silica. The excess of siliceous matter is believed 

 to be thrown out as a separate body of material usually con- 

 solidating as granophyre in a manner analogous to the sep- 

 aration of the excess of a salt in a saturated solution." C^) 



Remembering that the granophyric-diabase of Blinman 

 is likely to be a little more acid than the two rocks analyzed, 

 it seems probable that its composition would closely resemble 

 those in the above table, the chief difference, perhaps, being 

 a slightly greater content of alkalies and alumina. 



Its association with acid gneiss or rocks of the Cambrian 

 series, many of which are very acid, is also analogous to that 

 described by Tyrrell as typical for such rocks. It was hoped 

 to have had this rock analyzed for closer comparison, but un- 

 fortunately the specimen appears to have been mislaid. 



There is evidently at Blinman an opportunity for an 

 interesting investigation of this subject. 



Rocks associated with Basic Dykes near Blinman. 



A few notes are here appended on the rocks associated 

 with these basic dykes near Blinman. 



(1). "Contact Rock, up the. Creek from Horns Camp." — 

 A very fine-grained siliceous rock, light-grey in colour, and 

 with parallel bands of quartz. Microscopically the texture 

 is granoblastic. The constituent minerals are quartz, occur- 

 ring in roughly equidimensional grains, small prisms of 

 albite, with distinct multiple twinning, siderite or ankerite, 

 dusted with limonite and magnetite in fresh irregularly- 

 shaped grains. A few rounded grains of rutile also are pre- 

 sent. The grainsize varies in alternate bands from "05 mm. 

 to 002. Quartz and siderite occur in a small vein in the 

 rock, the latter being idiomorphic. This rock may be termed 

 an adinole. 



(2). "Purple Slate," from the same locality as the pre- 

 vious rock. — A finely-granular vesicular rock, rather heavy 

 and in appearance not unlike a weathered basalt. The 

 numerous vesicles, 2 to 3 mm. in diameter, are seen on a 

 fresh surface to be filled with a limonite paste; on exposed 

 surfaces they are quite empty. It is quite impossible micro- 

 scopically to distinguish the individual minerals of the base, 

 so exceedingly fine-grained is the rock. It appears, however, 



(7) Op. cit., p. 365. 



