occasionally on the pericline. The actinolitic hornblende mentioned in B 102 is not present here, but the groups of brown mica plates are rather more numerous.

(B 103.) Gneiss.—A white rock consisting of an even-grained mixture of quartz and feldspar, with a few plates of biotite. In the hand specimen a gneissic structure can be seen. Section: Quartz completely allotriomorphic; is very abundant. Feldspar generally twinned only on the Carlsbad law, but sometimes oligoclase on the albite law and frequently in smaller crystals, showing a further development of pericline twinning, giving an appearance almost similar to that of microcline. Slightly decomposed into grains that are for the most part muscovite plates. Biotite in fairly large grains is not infrequent; it is evidently an original constituent. A few grains of zircon and magnetite, and a little apatite.

(B 107.) Aplite.—Hard compact rock, light-green. Separate grains not distinct. Section: Quartz in irregular clear grains, allotriomorphic. Feldspar much decomposed. Decomposition products needles of a light-green colour, probably epidote, and plates apparently of muscovite. Optical properties not entirely lost by decomposition, and much is evidently orthoclase. Other crystals show albite and occasionally pericline twinning. Extinction angle of lamellæ small, showing the mineral to be oligoclase. The only ferromagnesian constituents are very scarce; biotite mica plates partly converted into chlorite. The green colour of the rock, which in hand specimens is conspicuous, is entirely due to the epidotic decomposition products of the feldspar. The specimen is penetrated by small microscopic quartz veins. The specimen has sandstone adhering to it, and is evidently a dyke rock.

(A 188.) Syenite.—Very compact, showing dark crystals of hornblende of even size arranged in a white feldspathic material, which weathers on the surface into a light-green tint. Section: Feldspar almost opaque owing to complete decomposition. Products of decomposition fine colourless needles, with low refractive index and very weak birefringence, probably kaolinite. No twinning can be detected in the small patches of feldspar remaining clear, so it is probably orthoclase. Hornblende much bleached, apparently originally brown. Absorption, α, light-straw colour, β, greenish-brown, γ, brown, γ > β > α In the bleached portion of the crystals there is barely any noticeable absorption. Cleavage traces much bent and distorted in longitudinal section.

(B 106.) Syenite.—Generally similar in section and hand specimen to A 188, but much finer-grained. It is evidently a portion of the same mass.

(B 104.) Diorite.—An even-grained light-green rock in which the hornblende and feldspar can be distinguished readily. Section: Feldspar twinned on albite and pericline laws. Extinction angle indicates a basic oligoclase or andesine. Very slight cloudiness indicates the commencement of decomposition. Hornblende light-green, showing the usual absorption. Quite fresh. Magnetite generally in irregular masses, but occasionally idiomorphic, is common. Apatite needles pierce through the hornblende.

(B 105.) Diorite.—Light-green rock, with white feldspar crystals and light green hornblende. Not porphyritic in habit. Section : Feldspars all plagioclase and giving extinction angles characteristic of andesine. Albite and pericline twinning common. Amphibole completely fibrous, with irregular terminations. Light-green in colour and slightly pleochroic. Fibres differ slightly in optical properties, showing a striated appearance between crossed nicols. Probably all secondary, the amphibole being actinolite. Magnetite in small grains occurs throughout the section.

(A 161, 193, 194.) Feldspar Porphyrite.—Dark-green base, with distinct light flesh-coloured phenocrysts of feldspar, of tabular habit. Sections: Feldspar phenocrysts twinned polysynthetically on albite law and Carlsbad. Maximum extinction angle on sections perpendicular to 010 32°, indicating a feldspar of a rather acid labradorite type. Thickly dusted with decomposition products, which from their high birefringence and colourless nature appear to be muscovite scales. Groundmass consists of feldspar microlites, apparently labradorite much decomposed contained in a fine-grained mixture of green amphibole and brown mica. The amphibole shows no crystalline boundaries. It is highly pleochroic in shades of green. Maximum extinction 18° with the cleavage. Structure fibrous. Mica in very small plates. No distinct outline. From their arrangement it is almost certain that the last two minerals are secondary.

(A 187.) Porphyrite.—A black rock with weathered surface, covered with rounded hard resistant knobs. Generally similar to the groundmass of A 161. Section: Feldspar fairly large grains, penetrated through and through with epidote needles. Optical properties can still be distinguished in some of the crystals, and prove them to be labradorite. Amphibole, where original, very light-green, with ordinary absorption and twinning; where secondary, bright-green and actinolitic. Brown mica in small plates, probably secondary. Magnetite generally scattered through the rock.

(A 156.) Forellenstein.—Light-grey rock, with undecomposed feldspar showing bright cleavage planes. Not porphyritic. Section: Very fresh feldspar without idiomorphic

boundaries. Twinned repeatedly according to albite and pericline laws, as well as Carlsbad. Lamellæ generally broad. Extinction angle in sections perpendicular to 010 high in a few instances, proving the mineral to be anorthite olivine with rounded boundaries. Irregular cracks penetrating it, bordered by magnetite, and occasionally serpentine. A few grains of hypersthene showing strong pleochroism associated with the olivine. A few scattered grains of magnetite.

Of the rocks described above, syenites have been mentioned in the Geological Survey reports as occurring in many distinct localities within the drainage-basin of the lake as intrusive rocks. The diorites, granites, gneiss, and forellenstein are similar to some of the types classified together by the Survey as crystalline schists. These rocks are particularly characteristic of the Sounds region, though the distribution of the different types has not yet been ascertained in any of the districts where they occur. The porphyrite is a type that has not been recorded within this district by the officers of the Survey.

From the descriptions given it will be seen, on reference to a geological map, that these rocks must have been derived from various sources. In the “Reports of the New Zealand Geological Survey, 1879-80,” p. 129, a map is given illustrating the results of an examination of the country to the north and west of Lake Wakatipu by Mr. A. McKay. In this map the nearest outcrop of crystalline schists to the lake is that in the Hollyford Valley. It is stated in this report that the depth of the Hollyford Valley is the cause of the appearance of these rocks. The report states that syenites occur as intrusive masses in many places between the Maitai and Te Anau series, and as several junctions of these two series are shown within the present drainage-basin of the lake their presence in the moraine was to be expected.

The country further to the north and east was examined by Professor Park in 1886-87 (“Geological Survey Reports, 1886-87,” p. 121). The map accompanying the report shows crystalline schists on the west side of the Humboldt Mountains, again outside the present drainage-basin. These are the only notices I can find of these rocks near the lake.

A specimen of a rock quite similar to the porphyrite was brought me from the Kawarau gravels, and, as this rock is from its nature certain to be local in its occurrence, it must, in the absence of other evidence, be taken as probable that the two rocks come from the same locality.

These results are of some interest, for the presence of the “crystalline schists” shows that, if the occurrence of these rocks is correctly mapped, the ice of the Wakatipu glacier must have been partly derived from an area now beyond the