From a long and careful study of the Brachiopoda I am led to offer some observations upon the two recently published papers by Dr. J. Allan Thomson which have appeared in this Magazine. In the case of Dallina I cannot agree with Dr. Thomson regarding the type of folding. He considers D. septigera (the genotype) and D. raphaelis as dorsally biplicate, D. floridana as dorsally uniplicate. Now dorsal biplication is brought about by the dorsal sulcus being superimposed upon a single dorsal fold. In D. septigera, as well as in D. floridana, a broad ventral sulcus is superimposed upon a dominant ventral fold; these two species, therefore, are, in my opinion, ventrally biplicate (as in Magellania flavescens and some others).

The distribution of land and sea implies that the earth's outer shell is in a condition of approximate hydrostatic equilibrium. Otherwise the equatorial regions should be girdled by a continental protrusion, or else each of the polar regions should be occupied by a continental bulge. The observed fact that the inequalities of the earth's surface exhibit neither of these conditions proves that the general ellipticity of the lithosphere does not differ greatly from that which would be assumed by a liquid spheroid having a similar distribution of density in depth. The incapacity—thus demonstrated—of the lithosphere to endure permanent stresses leads naturally to an inquiry into the conditions that maintain continents and mountain ranges above sea-level. Investigations based on the deviations of the plumb-line from the vertical and on the varying intensity of gravity indicate beyond doubt that the elevated tracts of the globe owe their support to a deficiency of density in their deep-seated foundations, while the great sunken areas owe their depression to a corresponding excess of density in the underlying rocks. Thus has arisen the conception of isostasy, a word which was coined by Dutton in 1889 to express the state of hydrostatic balance that maintains in position elevated and depressed columns of the lithosphere.

In a review in the Geological Magazine for 1913 of an important paper by Cumings on the development and systematic position of the Monticuliporoids, it was pointed out that the elucidation of the post-embryonic stages of that group conclusively proved them to be Polyzoa, and disposed of Kirkpatrick's contention that they were allied to Merlia, a recent siliceous sponge. Thus, further to prove the dissimilarity between the Monticuliporoids and Merlia is to flog a dead horse. Nevertheless we welcome the excellent figures by Cumings and Galloway of the microscopic structure of the two organisms showing that the skeleton of the one is formed of super-posed layers and the other of radiate spicules so adjusted as to form a mesh-work.

The economic resources of the Trias as a whole are not great, if we exclude the two main industries (bricks and gypsum), but they are of interest from a practical standpoint, so that a short summary will be given here.

It is generally agreed that the main plateau of Western Australia has probably stood above sea-level since the earliest geological times, and has perhaps been a land area since the Archæan. Marine deposits lie against its northern, western, and southern borders, but none are known upon the plateau itself; but through the depression of Lake Cowan Kainozoic marine deposits have extended northward into the Dundas Goldfield at Norseman. These marine deposits include a deep lead with sponges which were described by Dr. Hinde (Bull. Geol. Surv. W.A., No. 36, 1910, pp. 7–24, pls. i–iii) and some patches of limestone which occur on the surface around Norseman. They have been described by Mr. A. Gibb Maitland, 1908 (“Recent Advances in the Knowledge of the Geology of West Australia,” Rep. Aust. Assoc. Adv. Sci., vol. xi, p. 153, 1906), and by Mr. W. D. Campbell (“The Geology and Mineral Resources of the Norseman District, Dundas Goldfield,” Geol. Surv. West Aust., Bull. 21, p. 22, 1906).

A study of the local stratigraphy, tectonics, petrography, and palæontology leads to some conclusions as to the physiography of the epoch in this district. Even studied as a detached area it may be noticed that the Bunter or pebble deposits are west of the sandstones and marls. From the fact that the eastern limits of the first two are west of the marls, and the second (sandstones) west of the pebbles, and from the evidence of other areas, it appears that this purely local west to east succession is applicable to the whole British area, and it is well known that each member thins from north-west to south-east (as a whole). This is the sequence typical of aqueous deposits, and particularly of delta deposits, and at the same time indicates (in part) the direction from which the sediment came.

Having shown that the ‘railway-cutting’ valleys of the Goathland area exhibit anomalies of position seemingly irreconcilable with the view supported by Professor Bonney that they are vestiges of an ancient river-system that has undergone readjustments by the process of stream capture, I may now enforce the argument by exhibiting the contrast between the form and magnitude of the old and those of the new valleys in the same district.

In 1902 I published a paper, the outcome of several years' observation, on certain phenomena associated with the glacial deposits of the Cleveland area, which I attributed to the former presence of a series of temporary lakes and lakelets upheld in the recesses of the hills by the margin of a great ice-sheet occupying the greater part of the North Sea. This interpretation met with so wide an acceptance, even by those geologists familiar with the district who had previously attributed the glacial deposits to a marine origin, that during the succeeding thirteen years I have steadfastly refrained from replying to criticism, hoping by this abstention to keep the issues unclouded by a controversy that might at any stage develop an acerbity not always lacking in earlier discussions.

In the year 1852 John Brown, of Stanway, published a paper on the Copford deposits (Q.J.G.S., vol. viii, p. 184), and in this includes a letter from George R. Waterhouse referring to two ‘Beaver’ teeth and the metacarpal of a Bear. One of these teeth is described and figured, and is said to differ from the beaver in being larger and also in the direction of the enamel folds. This tooth is preserved in the British Museum of Natural History at South Kensington, and I have recently had the opportunity of examining it; but the second tooth I have been unable to discover, concerning which G. R. Waterhouse says it “scarcely differs from that of the European species”.

Cordierite was first found in Travancore at Teruwulla (lat. 9° 22′ N. and long. 76° 37′ E.) in a kind of diorite. In the hand-specimen the mineral appears as violet patches and spots. Monazite, magnetite or ilmenite, garnet and biotite with probably a little hornblende, occur in association with it. In the sections the mineral is found to contain numerous globular inclusions which are surrounded by pleochroic halos. The larger of these may be identified as monazite under the microscope. The mineral is itself pleochroic, light vibrating in the direction of the axis of mean velocity (Y) showing a pronounced violet tint. When light vibrates in other directions the plates do not show any distinct colour, but a faint yellow tint may be observed in some plates. When light vibrates in the direction of the Y axis the pleochroic halos round the inclusions disappear and assume the violet tint of the crystal plate. Cordierite is supposed to occur usually in metamorphosed sediments, and the pleochroic halos are regarded as due to the presence of organic impurities. But a sedimentary origin is out of the question in the present case. It is held by some that pleochroic halos are due to the presence of radio-active substances. I kept an Ilford Empress photographic plate exposed in a dark box to a crushed sample of the mineral for more than twelve hours, but on development the plate did not show any indication of having been affected by the mineral.