This paper presents a brief outline of the geology of the area shown in the map, Text-fig. 1, and a petrographic account of a small collection (eighty specimens) of its igneous rocks. The area is centred about 60 miles south-south-east of the southern end of Lake Tanganyika, and midway between Abercorn and Kasama. It lies at the headwaters of the Chambesi River, the source, or one source, of the Congo, on the high plateau of Northern Rhodesia at an altitude of 4,000 to over 5,500 feet. There is as yet no literature dealing with the petrology of North-Eastern Rhodesia, and the Rhodesian Copper Belt is too far distant (over 300 miles) to allow of any useful comparisons at this stage. It is interesting, however, to compare the rocks of this area with those of the Lupa Goldfield (1) in Tanganyika Territory, some 120 miles to the north-north-east.

(1) Reasons are given for believing that the holotype of Anthracomya adamsi Salter (the genotype of Anthracomya) has been correctly identified.

(2) It is shown that the horizon of this presumed holotype is near the middle of the Similis-Pulchra Zone, and is near if not identical with the horizon of A. hindi Wright.

(3) Anthracomya adamsi at that horizon has no close connection with A. modiolaris (from which it may, however, have been derived at a lower horizon). The distinction of these two forms is discussed, and it is suggested that among well preserved specimens only very occasional variants cause any difficulty in identification. The shells referred to A. adamsi. s. lat. by Weir and Leitch from the base of the Similis-Pulchra Zone (1936) are not considered in this paper.

(4) The relations of A. adamsi, A. hindi and A. warei are briefly discussed: in view of the limited distribution of the various species it is thought best for the present to retain the three specific names.

Although two years have passed since the British Association Committee on Rock Nomenclature and Classification reported in favour of using grain-size as an important factor inclassification, very few petrologists have accepted the Committee's invitation to discussand criticize the suggested scheme. This silence may be taken to mean consent; but in some quarters the older scheme, based on mode of occurrence of the rocks, still finds favour. It is instructive to inquire how far it is correct to speak of the scheme as new. Actually one does not have to dig deeply into petrological literature to realize that the principle of grain-size classification has been advocated for many years; indeed, it was the guidmg principle in some of the earliest scientific attempts at rock classification, notably in the well-known scheme elaborated in his Lehrbuch der Petrographie by Ferdinand Zirkel in 1866 and 1893–4. The reactionagainst the complete subordination of mode of occurrence found expression in the second edition of Rosenbusch's Mikro-skopische Physiographie (1887), in which the igneous rocks were divided into (1) deep-seated rocks, (2) dyke rocks, and (3) effusive rocks, each of these main categories being subdivided in terms of mineral content. In quite recent times A. Johannsen (1931)

The following faunal list provides a comparative summary of the Palaeoniscids of the chief Border Cementstone localities:—

Foulden.

Styracopterus ottadinicus (White).

Carboveles ovensi White

Aetheretmon valentiacum White

Aetheretmon valentiacum var. ovensi White.

Aetheretmon whitei sp. nov.

Strepheoschema fouldenensis White.

In my Catalogue of the Ammonites of the Liassic Family Liparo-ceratidae in the British Museum, now in press, I was obliged to discuss one of the commonest and most widely quoted of ammonite species, namely Schlotheim's Amm. capricornus.1 Clearly it was impossible to ignore this species, merely because “its precise application was not known”2 I am not only in agreement with H. Douvillé3 that it is of capital importance always to respect a specific [trivial] name, however much generic names may be changed, but among the foreign ammonites in the British Museum there were several different forms labelled Amm.

MOST workers on fossils at the present day try to conform to the International Rules of Zoological Nomenclature,1 but there are cases in which even the most conscientious palaeontologist may be in doubt as to whether any given article or recommendation of the International Code can justifiably be applied. Some workers, I may add, are forgetting that this code should be a good servant, and must not be allowed to become a bad master; again, while others are in favour of applying to the International Commission for standardization of almost every problem, many palaeontologists feel that the rules should not be relaxed except in very special cases. It seems to me of general interest to discuss some doubtful cases; for future workers may be guided by our difficulties, and the overworked Commission will eventually benefit by the discussion.

A striking feature of the geology of the Lizard is the occurrence of rocks very rich in, or consisting entirely of epidote; as bands parallel to the foliation of the hornblende-gneiss and the green schists of the Old Lizard Head Series; as lenticles caused by local enlargement of those bands; and sometimes as veins cutting the foliation, for instance on Polurrian Beach. The coast-sections at Mullion do not show great development of these epidotic rocks in the hornblende-gneiss but bands one inch thick occur. At Porthallow and north of Porthoustock there is an even smaller development of these rocks, but along the coast from Pentreath Beach southwards round Lizard Point to Cadgwith epidote bands and lenticles are abundant. Sir John Flett remarks in the 1912 Memoir (p. 50) on the perfection of this banding, “which cannot be paralleled anywhere else in Britain,” but he has told me that in Anglesey epidotic rocks approach them in abundance. These Anglesey rocks were described by Dr. E. Greenly in the Survey Memoir of that area (1919, pp. 108 and 109 inter alia).

The rocks about to be described are found in various parts of the eastern and south-eastern portions of the eucrite mass which forms the bulk of Barnavave Mountain. They are best displayed, however, between the 700 and 800 foot contours in the area just north of the large N.W. fault which crosses the region.1 The main characters of the normal eucrite are already well known from Sollas's now classical researches on the western side of the mountain.2 The normal eucrite of the eastern part of Barnavave is very similar to that occurring in the west. It is composed essentially of a diallagic pyroxene and a basic plagioclase, with or without a small but variable quantity of rhombic pyroxene (Text-fig. 1A). The plagioclase varies from Ab19An81 to Ab30An70, but the bulk centres round the more acid of these extremes. When subjected to metamorphism by the later acid intrusions, it shows very fine “clouding” and may appear black in hand specimen. The diallagic pyroxene is almost colourless in thin section but has a pale brown colour in thicker pieces. It has a % 1.680 ±.003, γ % 1.703 ±.003, γΛc % 41°, (+) 2V % 63°±4°, dispersion moderate p>v. Achemical analysis will be found on p. 477. In places it has a well defined schiller structure. The rhombic pyroxene (enstatite), when present, is colourless and non-pleochroic in thin section and also shows schiller structure. The accessory constituents include some titaniferous magnetite or ilmenite (normally enclosed in pyroxene). Apatite appears to be negligible in quantity.

The mudstones of the Manganese Shale Group are very similar in their characters throughout, but in the present work, greatest stress is laid upon the mudstones of one horizon—the Bluestone. This is about 5 ft. 6 in. thick, and occurs immediately above the manganese-ore band, which is 30 feet above the base of the group. From this horizon special metamorphic derivatives of the normal mudstones have been obtained from one locality—the lower end of the workings of the Hendre Mines on the north-west slopes of Moelfre, about 2¾ miles east 15 degrees south of the village of Llanbedr. There is no doubt that the types described belong to this one horizon, which is everywhere else remarkable for its uniformity of character. They always follow immediately on the manganese-ore band in the normal manner, without break, and their relationships with the succeeding strata are apparently the same as with the normal rocks. Also, with the exception of the calcite-bearing rock (p. 372), all the rock types are identical chemically.

An interesting paper has appeared in the Bulletin of the Eoyal Academy of Belgium, summarizing the general stratigraphy of the pre-Bukoban (i.e. pre-Devonian of Europe and pre-Katanga of Central Africa) rocks of Central Africa. It also includes a profile of the Basement Complex of Tanganyika. This note refers to the above-mentioned section of the paper only.