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Geology of the Provinces of Canterbury and Westland, New Zealand : a report comprising the results of official explorations

Igneous Rocks

Igneous Rocks.

The Canterbury Museum possesses a series of igneous rocks collected in this zone, which are very varied, ranging from a coarsegrained granite to a very fine-grained petrosilex. In the Geological Map, I have indicated the occurrence of granite in the isolated Mosquito Hill on the northern banks of the Haast river, but Mr. G. Mueller informs me that, according to his observations, the whole hill consists of blue clay slates with a capping of alluvium on the very summit. In 1863, when passing along the northern banks of this river, which, for some distance from the western base of the Southern Alps, had consisted of alluvium, I came, opposite the Mosquito Hill where I camped, upon a number of very large blocks of granite, mixed with some smaller fragments of clay-slate, showing convincingly, from their sharp edges and the manner of deposition, that they had not travelled any distance. Some of the blocks consisted of a very fine white hornblende granite with black and silvery mica, the latter in large concretions, and the hornblende crystals, also large and needle-shaped, which, from the contrast of colour, gave a very fine appearance to this rock. Another good-sized block with large crystals of felspar (orthoclose) and plates of mica, was traversed by veins of a fine-grained granite, the whole again crossed by veins of quartz. The clay slates were of the usual silky nature. The whole appeared to have either been brought by a slip from Mosquito Hill, or to be perhaps the remnant of a ridge which had once united that hill with a similar isolated hill lying opposite to it on the southern bank of the Haast.