In the course of work in collaboration with Dr. J. E. Hemingway on the petrography of the Dogger of North-East Yorkshire it has been found that brookite is widely distributed as a “heavy mineral” constituent in several different kinds of sediment. This is in agreement with results obtained earlier by myself alone in the study of sandstones from higher horizons of the Middle Jurassic in Yorkshire. Although it does not yet appear that the distribution of brookite in the Dogger is of any particular significance, nevertheless the mineral itself shows interesting peculiarities and variations; a detailed discussion of these would be out of all proportion in the paper which we hope to publish shortly on the character and distribution of the Dogger in general; and it has therefore been decided to give here a brief and mainly mineralogical account of the different varieties of brookite met with, without discussing the general problem of the abundance of titanium minerals in the Yorkshire Jurassics and their local distribution.

The grits which occur intercalated among the Harlech Grit Series have very similar lithological characters throughout. In the field the individual grits are very persistent laterally and can be traced over large areas. During the course of work on the man-ganiferous members of this Series one such grit horizon, which has been termed the “Bluestone Grit”, and which occurs about 5–6 ft.

Although British and American forms of this genus all bear points of resemblance to Temnocheilus ventro-concavus, only two small specimens from Eastern Europe, Nautilus dorso-armatus Abich, resemble it in their possession of a flattened concave venter and a whorl section of quasi-quadrilateral shape.

(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.

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.