Mrs. E. Lort-Phillips, during her journey in Africa, collected some well-preserved Arca-like shells from a riverbed at Bihin, in Somali-land, which have been entrusted to me for determination. The specimens, belonging to one species, are of various sizes, quite black in colour, and covered in places with a lightish-brown matrix.

In the Palæontology of the Vertebrata, so much has been accomplished on the American Continent within recent years, that any European interested in this line of research is naturally attracted to the Museums and collections across the Atlantic. Among others, the writer of the present notes has at various times been desirous of comparing certain American and Canadian discoveries with those now familiar to workers in the Old World; and this desire having lately been gratified, it may not be uninteresting to offer a few remarks on the collections of extinct Vertebrata in the New World, viewed from the standpoint of one who has had the privilege of visiting many of the corresponding collections in Europe.

The genus Brachymetopus was founded by McCoy in 1847, and the generic characters were drawn from the Australian species Br. Strzeleckii, McCoy, which was at the same time described. The specific characters of this form were very briefly given, the leading features having been mentioned in the diagnosis of the genus. Dr. Henry Woodward in 1884 gave a new summary of the generic characters differing somewhat from that originally furnished by McCoy, being modified in such a way as to include the European or British species, Br. ouralicus, De Vern., Br. Maccoyi, Portl., Br. discors, McCoy, and Br. hibernicus, Woodw. The original type-specimens of Br. Strzeleckii used by McCoy (op. cit.) in drawing up the description of the genus, and figured by him at the same time, are in the Woodwardian Museum, to which they were presented in the year 1844 by the Rev. W. B. Clarke. They come from the Carboniferous Shale of Dunvegan, New South Wales. The specimens comprise three complete head-shields, two of which are hollow impressions and one a cast, and portions of three or four others; there are also three casts of complete pygidia, one perfect impression, and fragments of two others. This material demands a fuller description of the specific characters than McCoy furnished, particularly as this type-form of Brachymetopus shows features differing in several respects from those of the better known European species ascribed to the same genus. McCoy's description (op. cit.) of the species was as follows:—

“Glabella widest at the base, with one very minute, obscurely marked, cephalothoracic furrow at the base on each side; all the segments of the pygidium with an irregularly tuberculated ridge along the middle; lateral segments forming large tubercles where they join the thickened limb, opposite each of which is a short slender spine projecting from the margin”.

Some specimens of dark olive-grey mudstone from Peeblesshire, collected and shown to me by Mr. D. J. Brown, contain several internal and external casts of small bivalved Entomostraca.

In the year 1878 there was a short controversy between us respecting these beds in the pages of this Magazine. Since that date we have both enlarged our knowledge of the beds at the junction of Chalk and Greensand, and recently we have had an opportunity of meeting at Seaton in Devon, and of examining the Whitecliff and Beer Head sections together. The result of this and of friendly discussion is that we have both modified our views and have come to an agreement on the most important points about which we differedin1878. Under these circumstances we think it will save trouble and facilitate future enquiry if we jointly express our present views on the subject so far as we are in agreement.

1. Chloritic Marl.—As far as we can ascertain, this name was first applied to certain beds at the junction of the Chalk and Greensand in the Isle of Wight It was subsequently adopted by Prof. E. Forbes, for a bed which occupied a similar position in Dorset, and has since been used for any bed lying at the base of the Chalk Marl and containing fossils and green grains.

The structure of mountain ranges has always been difficult to understand. They often show that peculiarly complicated disturbances of strata have occurred in the process of their formation. Mountain ranges in many stages of dissection are to be seen in various parts of the world; but the better knowledge which their study has furnished us with has not, at the moment, always assisted us in the better understanding of the problem of mountain building.

In Appendix I to the Summary of Progress of the Geological Survey for 1921, pp. 118–28, “The Retreat of the Lake District Ice-cap” is dealt with.

The geological succession of the rocks of the N’Changa District is so typical of that of the Northern Rhodesia Copper Belt as a whole, and indeed of much of the Colony of Northern Rhodesia, that it is felt that a summary of the sequence of events which together make up the geological history of the district may serve as a contribution to the geological literature of the general Northern Rhodesian field. For a fuller account of the details of the petrography and mineragraphy of the rocks and ores of the N’Changa District reference should be made to Bancroft and Pelletier (1929), and Jackson (1932).

Shells with the external aspect of Bouchardia have been known for some time from the New Zealand Tertiary (Oamaruian), and were first described by Hutton in 1905 under the names of Bouchardia rhizoida and B. tapirina. The correctness of this generic ascription was doubted by von Ihering, who stated that the shells lacked the characteristic external form of Bouchardia. In this, however, von Ihering was mistaken, probably owing to the unsatisfactory nature of Hutton's figures, for these species agree externally with Bouchardia in the very characters which he supposes they lack, viz., the very sharp beak ridges, the more or less straight sides, and the presence of a longitudinal cord over the suture of the deltidial plates. The most characteristic external feature of the shell of Bouchardia is that the sharp beak ridges unite in an apex dorsally of the foramen, i.e. the foramen is epithyrid. In Hutton's supposed Bouchardiæ the foramen is permesothyrid, but almost epithyrid.

Dolomite is common in parts of the Chalk Group of North Sea petroleum reservoirs. The stratigraphic distribution, microtextures, and stable isotope ratios of dolomite vary both within and between four of the North Sea chalk fields examined in this study, the Eldfisk and Tor of the Norwegian Sector, the Dan Field of the Danish Sector, and the Machar Field of the United Kingdom Sector, indicating that the conditions favourable for dolomitization occurred at different times and places in the North Sea Central Graben. Dolomitization in all of the examined fields occurred late during diagenesis, after significant compactional grain breakage. Dolomite precipitation in the Eldfisk, Dan, and Machar fields occurred in modified sea water, which had Σ18O values between the assumed Cretaceous/Tertiary seawater value −1 and +8‰ (SMOW). The enrichment in 18O was probably the product of calcite recrystallization at elevated temperatures in a low water/rock ratio system. The timing of dolomitization varied with respect to organic diagenesis; dolomite precipitation in the Eldfisk Field coincided with bacterial methanogenesis whereas dolomite precipitation in the Machar Field probably coincided with bacterial sulphate reduction. The magnesium in the dolomite may have been derived from the neomorphism of high magnesium calcite to low magnesium calcite.

The fractography and conditions of propagation of joints that cut Devonian siltstones in the Appalachian Plateau, New York, and Eocene chalks from the Beer Sheva Syncline, Israel, are investigated. The joints cutting the siltstones are marked by S-type and C-type plumes, and the joints cutting the Lower Eocene and Middle Eocene chalks are marked by coarse and delicate plumes, respectively. The four plume types propagated under sub-critical (slow propagation) conditions. On the semi-quantitative fracture velocity (v) versus the tensile stress intensity (KI) curves, the S and C plume types fall in the KI=0.073–0.79 MPa m1/2 and v=2×10−4–10−2 m/s and KI=0.073–0.79 MPa m1/2 and v=10−6–10−4 m/s ranges respectively. The coarse and delicate plumes fall in the KI=0.03–0.17 MPa m1/2 and v=10−6–4×10−5 m/s and KI=0.03–0.17 MPa m1/2 and v=10−4–5×10−3 m/s ranges, respectively. Generally, slow plumes are relatively short, show periodicity, and typically exhibit superposition of arrest marks. On the other hand, faster plumes are longer and continuous, occur particularly in thinner layers, and show no superposition of arrest marks. There is a clear distinction between two en échelon segmentation end-members in the joint fringe, the ‘discontinuous breakdown type’ and the ‘continuous breakdown type’. There are also ‘transitional’ variations between the end-members. Only curved ‘discontinuous breakdown type’ boundaries of en échelon fringes can be equated with mirror boundaries.

Zoœcia large and pentagonal, average length about 8 mm., markedly crater-shaped (i.e. with side walls sloping inwards to a deep-lying areal opening): areas sub-pentagonal as a rule : side walls wide, sloping inwards practically all the way from the zooecial margin, the slope gentle in the lower half, then changing gradually to quite steep at the upper end; the two upper corners are occupied by a pair of stumpy perforated tubercles; just below the summit of the steep inward slope at the upper end of the arc, close to the corners and probably communicating with the external tubercles, are two pores so faint as to be hardly visible in full light.

In many coalfields in the zone of Anthracomya pulchra and Carbonicola similis there is a marine band, viz. Mansfield, Yorkshire; Dukinfield, S.E. Lancashire; The Gin Mine, North Staffordshire; Rimbert, North of France; but, apart from a doubtful Lingula from the roof of the Brassy coal at Bersham Colliery, no marine fossils have previously been recorded from undisputed Coal Measures of the Denbighshire Coalfield.

A network texture made of graphite with calcite filling the holes is described from an area of staurolite-garnet grade of metamorphism. It is pointed out that this is the earliest texture preserved in the rock, and that it resembles a cellular structure and may therefore be of organic origin, possibly a primitive plant. At present, however, it is not certain that the structure is organic in origin.

A simple seismic refraction line some 115 km long has been made across Norfolk to provide constraints on the depth to the ‘igneous/metamorphic’ basement. Shots were fired in the Wash and off the coast near Lowestoft and attempts were made to record at approximately 2 km intervals along the line. Recording quality was only fair, resulting in incomplete coverage of the line, and this restricts the quality of interpretation. The results show a refractor of about 6.05 km s−1 revealed over the whole line with no first-arrival evidence of the 4.5–5.5 km s−1 velocity expected from Palaeozoic sediments. Using estimated velocities of 2.4 km s−1 for the post-Palaeozoic succession, 4.5–5.5 km s−1 for the Palaeozoic succession and an estimated sub-crop position of the basement on the sub-Mesozoic floor, models are produced which suggest that the Palaeozoic sediments are no more than 600–1500 m thick at the eastern end of the line, depending on the Palaeozoic velocity assumed.

Many years ago, and before I entered on my duties in the Edinburgh Museum, the late Mr. C. W. Peach pointed out to me a specimen in the Hugh Miller Collection, which he was inclined to consider as new. It was a Cromarty nodule with dislocated remains, including a dorsal and a pectoral spine, of what was apparently a Diplacanthns of unusual size.

The Cretaceous System of England, according to A. J. Jukes-Browne1 is “naturally divisible into two distinct and different series of strata”, namely a lower series consisting chiefly of sands and clays, and an upper series, consisting mainly of chalk. The succession on the whole is easy to unravel, and was correctly described (even before the name Cretaceous had been thought of) by Webster in his Letters, written in 1811 and published in 1816 in Sir Henry Englefield's Isle of Wight; it is almost exactly the same as we recognize it to-day. Two slight changes have been made, but they have been considered by some to be changes for the worse. Firstly, the beds to which the name“Greensand” had originally been applied by Smith and Webster2 are now called “Upper” Greensand, a term that has given rise to much confusion3; and, secondly, the “Ferruginous Sands” are now known as “Lower” Greensand, a name that was strongly condemned by workers like Fitton, Godwin-Austen, and Judd. It is on record4 that even Jukes-Browne admitted that he had long been endeavouring to do away with the awkward and misleading terms “Upper” and “Lower” Greensand ; but these names, though better not used without locality, have now become too familiar and are too useful for mapping to be abandoned entirely in favour of the more precise stage names Cenomanian, Albian, and Aptian.

The generic name of the Sauroid Fish, here indicated by portions of jaws, relates to the unusually well-marked arrangement of the teeth on the dentary bone in two almost parallel ranks along the whole of its alveolar border. The outer rank (Plate V. fig. 1) consisting of few and large teeth; the inner rank of small ones in greater number.

Schists composed essentially of biotite and sphene have been found in many localities in the psammitic groups of the Moine Series in Ardnamurchan. From petrographic and chemical evidence it is concluded that they were heavy mineral bands, composed of sphene and iron oxides with a matrix which was partly pelitic and partly quartzo-feldspathic. This postulated original composition may have been produced by sedimentary slumping, for which field evidence is available. The unusual chemical composition was probably accentuated at higher grades of metamorphism by metamorphic metamorphic segregation, particularly a loss of soda or of segregation, particularly a loss of soda or of albite into the surrounding arkoses.