Abstracts of Papers Read Before Branches.
Earthquakes and Earthquake Prediction.
L. Bastings, D.Sc.
In recent times, the study of earthquake phenomena has come to serve as a valuable tool in the investigation of the structure of the interior of the Earth. Gravitational and magnetic evidence have suggested the idea that the deep interior of the Earth contains a large mass of metallic iron. This idea has found substantial confirmation from the study of records of distant earthquakes, from which it appears that this iron core occupies the centre of the Earth and has a radius of about 2200 miles. Whether this large mass behaves like a molten liquid or has the rigidity of a solid is still a subject of controversy. Other breaks in the continuity of the Earth's structure have been revealed by these studies. The most noteworthy of these breaks is one at about 300 miles below the surface; this is possibly due to transition from one type of rock-material to another. There are also several minor structural discontinuities in the crust within 50 miles of the surface; and some indications are appearing of the existence of a slight structural difference between the Pacific basin and the rest of the world.
In the popular mind, great interest always centres around the possibility of predicting a coming earthquake. In order to achieve this aim, a forecaster must be able to specify the locality, the time and the magnitude of the pending disaster. It can be said without hesitation that such a prediction has never been made, and probably never will be. So many incidental factors are capable of influencing both the time and the magnitude of a shock that there is little hope of sufficient knowledge ever being available to achieve this. It will be much more profitable to study the signs of growing strain in the crust, so as to estimate in advance the probable location of major disturbances. On such scientific knowledge we may then hope to base a sound policy in regard to building safety, commensurate with the indicated risks.
On Certain Properties of the Earth's Deep Interior.
K. E. Bullen.
The paper described the methods by which the author had arrived at values for the density and pressure variation within the Earth. A special feature of the results was the implication concerning a change in properties of the Earth's material at a depth of order 500–700 km. below the surface. Details may be found in
papers of the author cited below.* The author also considered the question of the variation of gravity within the Earth; the solution of this problem arises out of the density solution, and was the subject of the paper in the Transactions of the Royal Society of New Zealand of September, 1939.
Note on the density and pressure inside the Earth, Trans. R.S.N.Z., vol. 07, pp. 122–124, 1937.
Composition of the Earth at a depth of 500–700 km., Nature, vol. 142, p. 071, 1938.
On recent developments in knowledge of the Earth's interior, Acta Astronomica, ser. c, vol. 14, pp. 17–21, 1939.
The Mollusca of Stewart Island.
A. W. B. Powell.
(Rec. Auck. Inst. and Mus. vol. 2, No. 4, pp. 211–238, 27th Oct., 1939). The paper provides a comprehensive list of the Stewart Island Mollusca, 383 species being recorded, 21 of which are described as new. Five new genera and a new subgenus are proposed. Two external influences affect the fauna—the cold water, west wind drift and, to a lesser extent, the East Australian warm water current. The Subantarctic element in the fauna is strengthened by eight additional records, the most noteworthy being a new species of Kerguelenia.
Pollen Grains of New Zealand Trees.
Lucy M. Cranwell, M.A., F.L.S.
In introducing a detailed account of pollen-grain morphology in the Coniferae and the Fagaceae, the two most important families of wind-pollinated trees in New Zealand, the author summarised the characteristics of wind- and insect-pollinated types, and described the technique of pollen-analysis through which a study of pollen, wind-borne to growing bogs and preserved in their successive layers, made it possible to trace back the history of forests for thousands of years.
Pollen grains of Nothofagus, Phyllocladus, Dacrydium, and Podocarpus had been found freely in our peats and lignites by the author, those of Agathis only once, while the preservation of Libocedrus pollen was considered doubtful. Distinct generic types existed, overlap occurring only between Dacrydium and Podocarpus because of the anomalous group created by D. colensoi, intermedium, and laxifolium. Nothofagus pollen was shown to be quite distinct from that of Fagus, and all species investigated from New Zealand, South America, and Australia fell either into the menziesii-moorei-obliqua group, or into the fusca-dombeyi group, the latter at present restricted to New Zealand and South America. There was no proof that Fagus grew in the Southern Hemisphere in Tertiary times.
Cranwell, L. M., 1939. Southern-Beech Pollens, Rec. Auck. Inst. Mus., vol. 2, No. 4, pp. 175–196.
— (in press). Pollen-grains of the New Zealand Conifers, N.Z. Journ. Sci. Tech.
[Footnote] * The variation of density and the ellipticities of strata of equal density within the Earth, Monthly Notices Roy. Astron. Soc. Geophysical Suppl., vol. 3, No. 9, pp. 395-401, 1936.
Tarawa, a Micronesian Atoll.
The extreme limitation of the resources of Tarawa, an atoll in the Gilbert Group, was described to provide an example of the simplicity and modification imposed upon a culture by a restricted environment. Shortage of timber and lack of variety in diet have developed ingenuity and ability in the exploitation of limited materials.
Coconut and pandanus, which comprise the major part of the scanty vegetation, form an important element in every activity and product in the community. A limited amount of dryland taro is the only cultivated vegetable. Dependence upon the sea for the animal food supply is an important influence in the life of the people.
The greatest example of modification is seen in canoe design, which has developed to a stage far beyond that common where large trees are obtainable. Under the stimulus of the necessity of using short, narrow timbers, a boat has been evolved unequalled anywhere in the Pacific for speed and grace.
Maori Wooden Bowls.
The paper described some 40 examples of wooden bowls in the Auckland Museum Collection.
Within New Zealand great variety of form is disclosed, ranging from crudely hollowed out logs to well finished examples. It is not possible on present knowledge to relate any given type of bowl to a particular locality. The wood most commonly employed, though not exclusively, was totara.
Unusual types were represented by a four-legged specimen from Motiti Island and a specimen from Hauraki Plains, in which the bowl rests on four peculiarly looped feet.
Smaller utensils of various shapes were numerous, some being used for pouring and others as platters. Of the former, most possess a spout carved out of the solid. Decoration, though not general, was usually confined to handles and spouts. An example from Waikato has the spout carved in the form of a head with a wide-open mouth. The handles of a Taranakian bowl have both been carved to represent conventionalised human faces.