—The field impression of a high degree of uniformity in the composition of the intrusive Karroo dolerites over a vast area is confirmed by new chemical and microscopical studies. The pyroxene characteristic of the dolerites is a typical pigeonite, which, however, does not display any twinning on (100). The plagioclase is potash-free, usually a labradorite, but it has been observed that a homogeneous crystal of plagioclase may be in twin position to another homogeneous crystal of a very differently composed plagioclase. The close resemblance of the doleritic liquid to the artificial liquid taken by Bowen to represent basaltic liquid is noted, and his conclusion that pyroxene and feldspar should crystallize simultaneously in natural basaltic liquid is confirmed.

Conceivably the doleritic liquid was quite original and not a differentiate of any earlier liquid. However, analogies like those with the tholeiites and similar hypabyssal rocks of Great Britain suggest that in South Africa, as in Great Britain, the liquids of these hypabyssal rocks were derived from the slightly more femic plateau-basalt.

On that assumption the question of the mode of differentiation arises. The fractional crystallization of plateau-basalt, as now described by Bowen and other leaders, does not appear competent to explain the abnormally low soda of one of the analyzed dolerites, nor the excess of soda and total alkalies in plateau-basalt respectively over the soda and total alkalies of the Karroo dolerite. Further, the settling-out of early olivine does not explain the excess of (total) FeO in plateau-basalt over the (total) FeO in the Karroo dolerite. The actual relations indicate the need of renewed examination of the theory of magmatic differentiation by crystal-fractionation. In any case many more data are required before it is possible to decide upon the precise relation of the Karroo dolerite to a parental magma. Possibly such additions to knowledge may annul present difficulties in the way of accounting for the composition of the dolerite.

Natural compact ice is not wholly crystalline. Salt solution is present in glacier ice at temperatures down to −21·72°, and is probably located at the intergranular boundaries. The proportion of brine is normally very small, but becomes considerable near 0°.

The special mechanical properties at the intergranular contacts, the “Hugi effect” on melting, the phenomena of regelation, and the infra-red absorption, indicate that the molecules at these contacts are in the amorphous state. This may be the case in ice free from salts.

Internal flow takes place by relative displacement of crystalline portions by means of slip:—

1. along the basal planes of the crystals,

2. along intergranular surfaces,

3. along fracture surfaces within the individual crystals.

Processes 2 and 3 are facilitated by the presence of liquid at the surfaces of slip, and it is the regelation power of this liquid which preserves the cohesion of the deformed masses.

The liquefaction at points of compression, transference of the liquid, and its congelation elsewhere, is an important factor in the formation of compact ice from névé, but is of secondary importance in the flow of compact ice.

The processes by which ice suffers deformation are those which operate in the flow of all crystalline masses, the comparative ease with which it is deformed being an instance of the weakness of rocks near their melting temperatures. Ice at hundreds of degrees below its melting point would compare in strength and hardness with the other crystalline rocks which exist under like temperature conditions in the outer part of the earth's crust.

For many years the writer has been specially interested in the variations apparent in the processes of weathering of rocks under different climatic and physiographic conditions, and has made several attempts to explain such features. Of these published attempts the most detailed took the form of a Presidential Address to the Royal Society of New South Wales in 1927. Certain portions of the argument were repeated in Economic Geology, but the regional aspects of the question were omitted.

At 10.17 a.m. on the 17th June a severe earthquake shook Wellington and dislodged the mirrors of the Milne-Shaw seismographs at the Dominion Observatory. As soon as the instruments were readjusted, the after-shocks indicated the epicentre was in the northern part of the South Island; and telegrams from all parts of the Dominion showed that Murchison village had suffered more damage than any other locality. Accordingly a number of Government Officers from several technical departments visited those areas where great damage was reported and on their return to Wellington a round-table conference was held on 26th June, in the room of the Hon. The Minister for Scientific and Industrial Research. In addition to investigations that would normally follow the earthquake, several other pieces of work were suggested at the conference or were subsequently undertaken.

Those who have made separations of heavy minerals from sands or crushed rocks will doubtless have realized that concentrates obtained by panning are not identical with those obtained when heavy liquids (usually bromoform) are used, for certain of the heavy minerals, either because of their shape or somewhat lower densities, tend to be washed away to a greater extent than zircon, rutile, etc. Yet, on account of the high cost of bromoform, panning is frequently adopted; and a compromise method of panning off most of the light material and completing the separation by means of bromoform is also used. As there is no record in geological literature (so far as I can trace) showing precisely to what extent the composition of the residue depends upon the method adopted, the following account may be of interest.

To meet the ever-growing needs of London for an adequate supply of water, the Metropolitan Water Board has recently constructed a new storage reservoir at Littleton, near Staines.