England has only had one Glacial Period. G. W. Lamplugh pointed this out in 1906 before the British Association at York, and quite lately also in 1913 before the International Geological Congress in Canada. No one has yet attempted to contradict it.

The chemical composition of the Barshaw bekinkinite has been determined by Mr. E. G. Radley, of the Geological Survey (Table I). In the Glasgow Memoir (pp. 134–5) Mr. Bailey points out the general similarity of this analysis to those of picrite, nepheline-basalt, and Hillhouse basalt, from the Lower Carboniferous of the Midland Valley of Scotland, and also to the type bekinkinites of Madagascar.The Barshaw rock, however, is distinctly richer in lime and alumina than the other Scottish rocks, indicating a greater richness in the anorthite molecule. This is well brought out in the calculation of the mineral composition from the chemical analysis (see later). The ultrabasic end-differentiates of the Scottish analcite rocks tend either to be enriched in the bisilicate minerals or in olivine. The former type includes the Barshaw bekinkinite, the picrites, and some Ayrshire theralites; the latter includes peridotites, kylites, and certain nepheline- and analcite-basalts. Chemically the bisilicate type tends to be rich, in lime and ferrous iron, and comparatively poor in magnesia, with, for the silica percentage, a rather large amount of alkalies. The olivinic types are rich in magnesia, with low silica and alkalies. In the American Quantitative Classification the Barshaw bekinkinite falls into the subrang III, 6.4.5 (named ‘papenoose’ by Lacroix), whereas the bekinkinites of Madagascar fall into the neighbouring eubrangs III, 6.3.4 (limburgose) and III, 6.3.5 (unnamed). The majority of the Scottish analcite rocks fall into limburgose (III, 6.3.4), monchiquose (III, 6.2.4), or camptonose (III, 5.3.4), subrangs whose clear relationships are shown by their numerical symbols.

In his report on “The Coal Resources of the East Africa Protectorate” published in the Twelfth International Geological Congress‘ The Coal Resources of the World (vol. ii, p. 381), Dr. J. W. Evans discusses evidence bearing on the existence of coal in the Taru Grits, which form the lowest member of the coastal series of sediments in the East Africa Protectorate. Referring to a report of mine, he remarks that I believe them to be of Karroo age, and then says, “E. Fraas, who subsequently made a brief examination of the line of railway, and whose account of the geology of the region differs in many respects from that of Maufe, refers them to the Middle Dogger (Inferior Oolite).”

In Professor Shand's reply to my criticism of his original paper on the application of the principle of saturation with respect to silica in the classification of igneous rocks, some points arise which make it clear that he has misunderstood me in several particulars. In the beginning of my paper, it was explicitly stated that what was to be considered was (1) whether the principle, as enunciated by Professor Shand, could be extended to minerals other than the silica ones (quartz, tridymite, etc.), the felspars and the felspathoids, and (2) whether the criterion whereby the rock minerals were divided into the two groups of saturated and unsaturated was sufficiently exact. The criterion used was that of “the observed facts of distribution”, and any mineral which was found coexisting with quartz or some other form of silica in igneous rocks was said to be saturated, while those which did not occur along with quartz were said to be unsaturated. Correspondingly, rocks which consisted entirely of minerals of the former type were classed as saturated, those consisting of mixtures of the two types as part-saturated, and those consisting solely of the second type as unsaturated. I endeavoured to show that the rock-forming minerals cannot be satisfactorily divided into two classes in this empirical fashion, without any consideration of the cooling-histories of the individual rocks in which the minerals may be found.

Professor Lacroix finally states his views on the age of various sorts of laterite, regarding it as probable that all the phenomena considered in his memoir are still in a state of active evolution, although no direct observation of this can be made, except in the case of ferruginous concretionary action at the surface of the cuirass. But he gives evidence to show that the process of lateritization must be a slow one. There are laterites of at least two ages, as proved by the eroded cliffs of ‘fossil laterite’ contrasted with the latérite d'alluvions of the valleys, these two types corresponding in position to our Indian high-level laterite and low-level laterite. He finally concludes that (p. 351)—

Although the so-called Crawfordjohn essexite has been mentioned several times in petrographic literature, no detailed description of the occurrence has been given. In 1888 Teall described the main rock of the intrusion as an abnormal variety ofthe N. W.-S.E. Kainozoic dykes and noted the porphyritic augite andthe abundance of felspar, olivine, and apatite. Lacroix, in a generalpaper on the teschenites, mentioned the occurrence of nephelite in the same rock, which he described as an “olivine-teschenite, passing instructure to a tephrite”. Bailey, in the Glasgow memoir, remarked on the close similarity between the Crawfordjohn and Lennoxtown rocks and classed them with the essexites on account of their chemical similarity to the Brandberget rocks, while Tyrrell, on account ofthis similarity and also of the resemblance to the Carclout essexite, included them in the late Palaeozoic alkaline group.

Introduction.—The following account of the alteration produced in shale by the sill-like intrusion at Marston Jabet, near Nuneaton, supplements the more general paper dealing with the intrusion as a whole. (See GEOL. MAG., April, 1915, pp. 162-8, Plate VI.)

The resemblance of the oral face of an Edrioasteroid to an Asteroid has not merely been remarked on by nearly every writer on the group, but has led many of them to far-reaching conclusions (e.g. Steinmann, 1888 ; Neumayr, 1889). None the less no exact comparison of the structures has yet been made ; nor indeed was such possible until accurate descriptions were available. These have now been provided for various recent and fossil Asterozoa by many writer referred to in the sequel, and especially by Mr. W. K. Spencer (1914, “Monogr. Brit. Palæoz. Asterozoa” Palæontogr. Soc).

Last year I received from Colonel Freire d'Andrade a number of interesting alkaline igneous rocks, from a valuable collection made by him during an extensive exploration in North-Western Angola undertaken some years ago. Until recently our knowledge of the geology of that part of Africa was very scanty. Already in 1897 Cornet had described the western tongue of the Belgian Congo which separates the Portuguese provinces of Cabinda and Congo. Moreover, the occurrence of copper ores at Bembe and Senza do Itombe had attracted some geological attention, but it was not until Colonel Andrade's journey that any systematic geological observations were made over a large area of the territory. Since then a number of prospecting expeditions have been conducted by J. J. MacHugh, the results of which serve to extend our knowledge to the south of the area described by Colonel Andrade. In view of the inaccessibility of much of the literature dealing with Angola, it may be interesting, before giving petrological details of some of the rocks, to present in English a short sketch of the geology of part of Portuguese Congo and Loanda, embodying the observations made by Andrade and MacHugh.

The rocks described below were collected by Colonel Andrade, in 1904, on the road which begins at Senza do Itombe on the Loanda-Malanji Railway, and runs in a north-easterly direction to Bango.

Olivine Ulrichite. — Megascopically this rock differs from the foregoing nepheline monchiquite in having a well-marked porphyritie structure, the phenocrysts including orthoclase and nepheline in crystals having a maximum dimension of nearly a centimetre. Under the microscope the minerals present are :—