Over a period of some three years Dr. A. W. Groves has been working on the correlation of intrusions by their heavy mineral content, and the results have been published in three papers which have appeared in recent volumes of the GeologicalMagazine. The three papers read seriatim provide an interesting study of the evolution of an hypothesis which, if substantiated, would remove much, and in certain favourable cases, all of the uncertainty that usually shrouds the age of an intrusive rock-body.

The weathered surfaces of the limestones and calcareous shales of the Lower Lias in Somerset and Dorset sometimes exhibit curious paired markings. On careful examination these prove to be cross sections of U-shaped burrows of organic origin, appearing as two circular markings connected by a shallow depression or by a slight variation in the character of the matrix. Similar burrows have been described from the Lower Estuarine sandstone of Blea Wyke, on the Yorkshire coast. Dr. F. A. Bather has discussed their origin and structure in detail and has assigned them to the genus Arenicolites, which was established by J. W. Salter for “all worm burrows with double openings”. Other species of the genus have been described from arenaceous and argillaceous beds of Longmyndian, Ordovician, and Upper Carboniferous age, but as far as the author is aware, the species here recorded is the first that has been mentioned from the calcareous rocks of the Lower Lias of England.

For many years composite minor intrusions, both sills and dykes, have been known from various parts of the world and most petrologists must have speculated as to the probable effect produced in the event of such composite intrusions having reached the surface in the form of an effusion. For obvious reasons it has not been found possible to trace a composite dyke upwards into a lava flow. However, during the revision of 1 inch Sheet 30 (Renfrewshire) for the Geological Survey, the author encountered, in the neighbourhood of Inverkip, a small village on the Firth of Clyde south of Greenock, certain peculiar lava flows which are believed to represent the effusive equivalents of composite minor intrusions. These “composite lavas”, which form the main subject of the present paper, are of Lower Carboniferous age (Calciferous Sandstone Series) and occur interbedded among the more normal flows towards the base of the volcanic group. Two distinct rock varieties, one highly porphyritic, with large phenocrysts (up to 1·5 cms. long) of basic plagioclase, and the other non-porphyritic, are associated within the same flow. The porphyritic type always forms the upper part of the flow and overlies the non-porphyritic; the junction shows unmistakable evidence that both were in a fluid state along their mutual contact at the time of emplacement.

Skerryvore consists of acid gneiss with dark bands containing biotite and hypersthene. The mica was probably formed by the recrystallization of chloritic matter by heat from an underlying plutonic mass. The islet is cut by a 2 foot north-south dyke of olivine-dolerite.

Dubh Artach forms part of a sill of ophitic olivine-dolerite and is probably of Tertiary age.

Sule Skerry consists of andesine-anorthosite into which dark streaks consisting of hornblende and quartz have been injected at a later date to form a banded gneiss.

As is well known, there is a great diversity of opinion with regard to the relationship of the implement-bearing beds of the Pleistocene formations and the Chalky Boulder Clay. Any facts which throw light on this vexed question might, I thought, be very acceptable and useful and I am endeavouring in this paper to bring forward what evidence I can bearing on this very difficult and perplexing subject.

In 1928 Dr. P. Tesch published a note on the occurrence of an igneous rock in Dutch Coal-measures (1).1 As this is the first occurrence of an igneous rock in Holland, the present authors have decided to publish a more detailed petrographical description of the rock, together with an attempt to correlate it with similar rocks in Great Britain and Germany.

The classification and nomenclature here adopted is that of Clark (1925), which should be consulted for the early literature; only those references which give recognizable figures are here quoted, although an attempt has been made to interpret the identifications given by Fourtau. The investigation has been facilitated by the collection of recent echinoids made by Dr. Macfadyen in the Farsan Islands; and my thanks are also due to Mr. C. C. A. Monro for permission to examine material in the British Museum (Natural History).

During an intensive investigation of the joint phenomena of the South Leicestershire igneous intrusions a widened joint cavity eighteen inches long and five wide apparently filled with “calcite or quartz” was noted. On closer examination the mineral showed perfect trapezohedra of analcime and cube-like rhombohedra of chabazite. The analcime crystals attained a diameter of 0·4 inches: they comprised the bulk of the specimen, the chabazite being very subordinate and only in small sizes. As is usual the analcime had preceded the chabazite in order of crystallization. The cubic mineral was colourless, milky white, and also reddish through impregnation with iron oxide. The chabazite was opaque white but translucent on fracture.

In a previous paper published in the Geological Magazine, the writer made an attempt to discuss the mechanism of earth movement on a continental scale purely from a tectonic point of view. The problem is so vast and involved that some of the vital points were hardly touched upon, partly because of lack of space and partly of literature. The arrival of the admirable works of Dr. A. du Toit and Dr. E. Krenkel has enabled the writer to deduce the mechanism of the movements of South Africa directly from its tectonic features, which process is thought to be far more reliable than the type of argument used in the previous case although the results arrived at are essentially the same. The earlier movements in North America are now seen to furnish evidence of the same type of mechanism as that which staged the later movements. An epsilon type of structure has been recognized in Eastern China, which was then described as a mere arc. The problem of the distribution of concealed coalfields in England was in the previous paper barely touched upon. It is now proposed to consider some of the critical points bearing on the problem.

I venture to present before the Section a new interpretation of the Scottish Caledonide structure. This essay is based partly on the impressions that I got on a short visit to the Northern Highlands and on a most instructive excursion to Ballachulish under Mr. E. B. Bailey's inspiring guidance; partly on my own experience of the tectonics of Central European crystalline regions; but of course, above all, on the work of many Scottish geologists.

A Specimen in the Ludlow Museum, which appears to he the lost type of Sowerby's species Orthoceras attenuatum figured in Murchison's Silurian System, plate 13, fig. 25, p. 632, from the Wenlock Shale of the “banks of the Onny River, near Stretford Bridge”, has been recognized by Mr. T. D. La Touche in rearranging and cataloguing the collection of local fossils. Owing to the fact that the large piece of rock (D. b. 49 in La Touche's catalogue) on which it occurs was fastened down to a tablet so as to expose only another specimen of a smooth and different species of Orthoceras, it had been completely hidden from view, as it was on the lower side. The specimen not only agrees in size, general characters, and rate of tapering with Sowerby's figure (though the annulations are sharper and narrower than there indicated), but it was also collected by Dr. Lloyd, as was the type, as stated by Murchison. The horizon (Wenlock Shale) is recorded on the existing label, but not the locality. However, Mr. La Touche, from his intimate knowledge of the rocks of the district, considers that the locality may well be that given by Murchison. A small portion of the upper end of the shell is now missing, corresponding to the imperfect non-annulated piece shown in the figure, but it seems to have projected freely out of the matrix, so it may easily have been broken off. Otherwise the specimen is in the same good condition as when Sowerby drew his figure, and we can have scarcely any hesitation in identifying it on the strength of the above evidence.

IN the interior of Africa, in the high region of the Portuguese colony of Angola, in localities lying at an altitude of from 3,000–4,000 feet, where the soil consists of a thick layer of sand, clearly derived from the disintegration of the underlying sandstones, one constantly meets with peculiar and interesting out-crops of iron ore in the form of brown ironstone (limonite) of a spongy texture. This brown ironstone has in some places a greyish metallic colour, in places a reddish-brown, brown, brownish-yellow, or other tint characteristic of this hydrated iron oxide, but in structure it is different from all other varieties of this kind of iron ore. The entire mass is full of irregular cavities exactly like those in an ordinary toilet sponge or in pumices, and gives the impression of a ferruginous mass inflated with gases. It also recalls the unforged iron produced in the old-fashioned methods of “burning out” metallic iron direct from the ore used by ancient metallurgists.

WHILST studying the Bibette Head Granite, the writer had occasion to devote a certain amount of attention to the rocks with which it is in contact. In the region under consideration, these are essentially of dioritic type. The Orbicular Diorite was first found in a small embayment forming part of the west side of Corblet's Bay. It was found later in a less well developed fashion, at Saye Bay. It is quite possible that extended search would prove the presence of more. For the most part the orbicules are widely scattered, but a boulder was found at the Corblet's Bay locality which shows several associated with inclusions of a more basic rock. This boulder is now in the Sedgwick Museum, Cambridge.

THE inlier of Carboniferous Limestone, situate within the Coal Measure area at Upper Vobster, was the subject of much controversy in the past. It was not, however, until 1912 that Dr. T. F. Sibly settled this vexed question, and showed that the inlier was a mass of Carboniferous Limestone and “Millstone Grit” superimposed upon folded Coal Measures by thrust-faulting. His paper contains a very accurate map showing the extent of the quarries and strata exposed at the time: the latter now unfortunately having been removed by further quarrying.

FOUR years ago Klemm (1926, pp. 111–15) showed that the 1 so-calledbeerbachites and gabbro-porphyrites of the Odenwald are not, as was previously supposed, dykes cutting the Frankenstein gabbro, but hornfelsed (granulitized) inclusions in the gabbro. Within the last few months has appeared the Geological Survey Memoir on the last ofthe great Tertiary igneous complexes that awaited detailed study in Western Scotland (Richey and Thomas, 193Oa). In this publication the authors have given much new information on the nature and mode of occurrence of pyroxenegranulite hornfelses associated with gabbros. Similar rocks are well known from the earlier work of Harker, Thomas, Bailey and others, on the Tertiary gabbros of Skye and Mull (Harker, 1904; Thomas and Bailey, 1924).

The following is a tabular summary of the rocks of north-eastern Antrim.

I have read with very great interest Dr. Peacock's paper on the distinction between palagonite and chlorophaeite in the GeologicalMagazine, for April, 1930. On p. 170 thereof, Dr. Peacock gives a brief summary of my conclusions upon the nomenclature of chlorophaeite and palagonite as given in my paper on the same subject. Briefly, my conclusions are that as far as can be judged from existing analyses, the hydrous glassy material forming a portion of the rocks originally called palagonite has a composition that brings it within the range of composition exhibited by various specimens of chlorophaeite, and that, therefore, the term palagonite should be reserved for the impure rock, and the term chlorophaeite used for this hydrous glassy material. It was also recommended by me that the process by which in the case of the basaltic tuffs the primary glass becomes hydrated should be termed palagonitization and that the same term should be applied to the process by which the interstitial glass of basaltic lava flows is altered with production of chlorophaeite. The fact that olivine, if present, a portion of the augite, and occasionally some of the felspar, may also suffer similar alteration or be replaced, is not regarded by me as pointing to an essential difference in the two processes.

The collection of rocks from the Sahara to be discussed was made by Captain D. R. G. Cameron, of the Royal Scots, during a journey across the Sahara from Kano to Algeria. The journey is described by Captain Cameron in his book A Saharan Venture (1928) and in a paper published in the Geographical Journal (lxxi, 1928, 538–59). The specimens were not collected in situ, which reduces their value somewhat. When one considers, however, that the collecting area is desert country where outcrops are comparatively scarce it is apparent that conclusions based on pebbles are not without value.