AT the present time most mining geologists appear to be in general agreement on the principle that primary ore-deposits are derived from igneous magmas. Furthermore, it is now almost universally recognized that the segregation and concentration of the metals and their compounds into payable ore-deposits is but part of a larger and more fundamental problem, namely, the differentiation of the igneous rocks, a problem which has exercised the ingenuity of petrologists for many years past and is still by no means solved. Unfortunately most of the speculations and theories put forward in explanation of these phenomena are in the main founded on facts and inferences derived from the study of the silicates; comparatively few petrologists have taken into account the behaviour of the oxidic and sulphidic compounds of the useful metals, which are commonly regarded in the light of rare and accidental constituents of the magma, rather than as having any particular bearing on the point at issue. The most notable exception to this general statement is Vogt, whose work on slags and ore-deposits is of an epoch-making character from the theoretical point of view, as well as of immense practical importance in smelting and blast-furnace practice. However, within the last few years great attention has been devoted by mining geologists to the subject of the genesis of ore-deposits, mainly because of its bearing on the question of persistence in depth or the replacement at lower levels of one ore by another, such as is known to occur in certain cases. It may be suggested, therefore, that the time has now come when it may be possible to attempt to combine the facts hitherto discovered along different lines of research into a coherent whole.

OUR knowledge of the fauna contained in the Lower Devonian beds of England is extremely imperfect and unsatisfactory, partly owing to the scantiness of the material which has been collected, and partly to the poor preservation of most of the fossils themselves. The lists of genera and species given in the Survey memoir (Explan. Sheet 350) dealing with the Torquay district are not extensive, and in many cases the determination of the species or even the genera is open to doubt. Correlation in detail with the well-established and richly fossiliferous Lower Devonian of the Continent is almost impossible in such circumstances, but Kayser in 1889, on the strength of the palæontological evidence which he obtained on the spot, correlated the beds at Meadfoot with the Lower Coblenzian. The fossils which he collected and identified from this locality were the following Rhenish species: Zaphrentis oolitica, Rhynchonella daleidensis, Chonetes sarcinulata, Spirifera hysterica, Sp. paradoxa, Strophomena cf. Murchisoni, Pterinea costata.

THE interesting rock-type hornblendite occurs at the Vavasour Mine, though it has only a very small development. It covers an area of about 600 square feet and is cut by two of the apatitemica veins, which are so numerous at this locality. The rock was incorrectly marked amphibolite on the map in Guide Book 3, International Geological Congress, xii, 1913, facing p. 112.

The purposes of this short paper are to place on record and to bring to the notice of geologists a deposit of sands and gravels containing numerous marine shells which is exposed on the Durham coast north of Easington. Marine shells (Littorina, Cyprina, etc.) have been collected before from sands and gravels lying above sealevel on this coast, but the deposits containing them have usually been removed in the course of quarrying operations, and no collecion of shells has been preserved in any museum; it is therefore of interest that a deposit has lately been observed which can be examined at any time by geologists, and from which specimens of shells can easily be obtained. It is also of importance that the exact mode of origin of these particular deposits should be determined.

THE small but very interesting collection of Ammonites described in the following pages was obtained during the summer of 1919 by Professor J. W. Gregory, to whom the writer is indebted for permission to study them. There are seven specimens altogether, three of them fragmentary, and all probably originally pyritized, but now converted into limonite. Though immature or fragmentary, all the specimens were seen to have indications of suture-lines, so that their study promised definite results even if, at first sight, it was difficult to place the fauna in the geological sequence. Superficially, there was greater resemblance to the Lower Cretaceous fauna (with Phylloceras of the heterophyllum group and Lytoceras quadrisulcatum) described from East Africa by Krenkel than to the Sequanian fauna of Mombasa, recorded by Dacqué, and a large series of which is preserved in the British Museum (Nat. Hist.).

The mechanical constitution of a detrital sedimentary deposit is the aggregate result of the operation of a complex suite of physical laws which govern transport of detrital material by, and its deposition from, water in motion. These physical laws have been elaborately investigated by many workers, and while much remains obscure, important conclusions have been achieved. The detailed examination of the mechanical constitution of the sediments of the geological column has been neglected, although a few pioneer workers have obtained notable results. Sediments of economic value have received attention, but in the realm of pure geology workers have been slow to take up the investigation. Accumulating results indicate, however, that geologists would do well to devote attention to this line of research. Distinctive results are being obtained from sediments, which, even though they may not lend themselves at the present time to complete interpretation, from the point of view of reconstruction of the conditions under which the said deposits were formed, nevertheless bid fair to provide the geologist with another weapon in his armoury. Fluviatile deposits have been found to possess a mechanical constitution distinct from that of estuarine sediments, and the latter are again clearly differentiated, mechanically, from purely marine formations. It may be remarked, too, that the nomenclature in current use applied to the loose sedimentary deposits lacks that element of scientific precision so desirable and necessary if proper progress is to be made. Such terms as “sand”, “clayey sand”, “sandy clay”, and “clay” are at present employed by different writers in different senses, and some system of classification which would give definiteness to the meaning of these and similar terms appears to be urgently called for. The only satisfactory basis for such a classification must be a quantitative one, depending upon mechanical analyses of sediments. When a sufficiently comprehensive collection of comparative data is available it should be a simple matter to devise an adequate scheme for the classification of the loose detrital sediments.