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

Texture of Rocks and Position of Strata

Texture of Rocks and Position of Strata.

The strata under consideration, judging from their lithological character, can however be divided into two main divisions, of which the first consists of gneiss and mica schists, and other beds of a similar highly metamorphic structure; and the other, of silky and mostly light-coloured slates, alternating with fine-grained sandstones and felstones. The former is well developed near Lake Hall, south of the Paringa river; and the latter in Mount Greenland on the northern banks of the Mikonui. The rocks near Lake Hall consist of finegrained gneiss and mica schists with veins and dykes of granite, the latter often coarse grained—dipping at a high angle to the west.

Phyllites, altering to gneissic schists, also occur in this district. The principal locality in the other zone—a zone which I examined carefully, and which seems to cover the greatest extent of ground, but, by many gradations, appears to pass into the first—is situated on the northern banks of the Mikonui river. Bluish clay slates, with occasional beds of fine-grained sandstone, are here exposed in many spots. In Redman's Grully, they dip 60 degrees to the north-by-east. In some other places higher up the river, they are more inclined, and dip'to the north-east. They are full of quartz veins, mostly of small dimensions; but none of them, as far as I am aware, have hitherto been found of sufficiently auriferous nature to be worth working. Some of the most interesting localities in that neighbourhood, as, for instance, Mount Rangitoto on the southern banks of the Mikonui, are unknown to me, but the Canterbury Museum possesses a large series of specimens, collected by many intelligent friends of that Institution, page 258since my last journey in 1868 to the West Coast, from which it appears that the silky clay slates are altered in many localities by the intrusion of granites and syenites into micaceous and gneissic schist, the change from the one to the other being gradual and very instructive, as may be seen from a series of specimens.

It thus appears that there are at least two series of beds included in my Westland formation. Owing, however, to the short time at my disposal when at the West Coast, I was unable to separate these. One is probably of the same age as my gneiss granite formation, forming the western base of the Southern Alps, and the other of much later origin, the slates and sandstones belonging to it having, in their turn, become changed into metamorphic schists in many localities, by plutonic action.