In June last (1927) Mr. K. E. Williams and I received the following letter from Mr. R. Hecker, who is in charge of the Siberian Collections at the Geological Museum, Academy of Sciences, Leningrad:—

Breccias in general have been exhaustively discussed by W. H. Norton, and Bonney has fully described a large number of sedimentary origin. But since these papers were written attention has been drawn to certain fresh types of brecciated rock, and perhaps a briefer account than that in Norton's paper and one referring more particularly to British examples may be of service.

The original generic diagnosis is as follows:—

“Polypary cyathiform, composed of numerous independent and frequently bifurcating polypiferous branches, originating from the distal extremity of a short stem, which is likewise polypiferous and is terminated proximally in an irregular corneous expansion. Hydrothecae of the type of those of Dictyonema, biserial, sub-alternate.

“The chief peculiarity of this genus is afforded by the character of the stem, which is identical in every respect with the main branches, and, like them, is denticulate or polypiferous throughout the whole of its extent. It commences proximally in a flattened expansion, with irregular or frayed-out edges, possibly the remains of a disk or bulb of attachment.

“The mode of branching is rigidly dichotomous, the first two branches being formed by the sub-division of the main stem itself. Each arm branches and rebranches again and again in the same manner, at frequent and close intervals, composing an elegant cyathiform or fan-like polypary, very symmetrical in form. The branches retain their original width to their final division, which gives rise to two minute branches less than one-tenth of an inch in length.

The Exhibition Grounds, which include the site for the Empire Stadium as well as for the British Empire Exhibition, comprise an area of roughly 216 acres. The north-eastern boundary runs parallel with the Metropolitan Railway, and the North Entrance to the Exhibition is only a few yards south of Wembley Park Railway Station bridge. At or near the station the mean level is about 110 feet above O.D.; but the surface of the ground is uneven, and rises to 210 feet above O.D. at Wembley Hill, outside the south-western extremity of the Exhibition area. The Wealdstone Brook runs irregularly along the northern boundary in an easterly direction in the neighbourhood of the Amusement Park, but for the sake convenience its regular course has been slightly diverted at this point and an old lake filled up. The main sections to be described are north of the brook.

The selection of a base for the Devonian System has evoked much controversy, and summaries of the literature are given in several papers. The subject has acquired a new significance recently through the work of Ch. Barrois and his coadjutors in the north of France, and that of W. W. King and L. D. Stamp in England. The matter has been argued at length in the papers referred to, and it is impossible to appreciate all the factors involved without reference to them.

Aggradation of the bed of a river is a well-known and common phenomenon in certain circumstances, but in the present case a mountain stream, whose grade is to steep that waterfall are present, is found flowing along the top of a well-marked but very irregular ridge to tufa. This is found in a little stream near the village of Binn, known to mineralogists for the rare minerals which occur in metamorphosed Triassic dolomite not far away up the valley of the Binna.

There are two specimens, both exfoliated, which seem to be co-specific, and to belong to Sphenotus. The larger one is the worse preserved of the two, but the other shows some distortion by pressure; it retains the right valve, which however had its characters very much obscured. A third crushed and exfoliated individual from Gramadal Quebrada may also belong to the species.

The National Museum of Wales has not existed, as a working institution, long enough to have accumulated an extensive series of type and figured fossils, but since recent developments have rendered available for reference geological collections that were hitherto packed in store rooms, it is felt that the time is opportune for the publication of a note concerning the geological material which the Museum possesses, with special reference to the specimens that have been described or figured.

Recently Mr. A. Stuart (1927, PP. 545–57) has published an account of the variation in a large number of specimens of Volutospina spinosa from the Calcaire Grossier of Grignon. In his study of that group he emphasized the variation in the ontogeny of the individual, and suggested the importance of such studies in relation to the more philosophical aspects of biology and in relation to the application of ontogenetic evidence to the problem of classification. The group studied by Mr. Stuart was one in which the latitude of variation in any character was particularly small.

The area covered by this paper embraces the northern end of the Pennines—the uplands of Lower Carboniferous rocks centred about Alston, together with the low ground of the Tyne-Irthing gap to the north. It is bounded on the west by the Vale of Eden. The Pennine portion is separated structurally from the regions to the north and west by the Stublick and Pennine Faults respectively. The former trends E.N.E., it has a downthrow to the north and has resulted in the preservation of the string of Coal Measures outliers which form a connecting link between the Cumberland and Northumberland coalfields. The Pennine Fault, trending S.S.E., with a throw of several thousand feet to the west, brings the New Red rocks of the Vale of Eden against the Lower Carboniferous beds of the Pennine Escarpment. These two faults meet at right angles near Castle Carrock. To the south the Pennine Fault dies out near Stainmore, and another dislocation, the Dent Fault, trending S.S.W., develops, and eventually links up with the Craven Faults which have an E.S.E. trend. These four faults, as pointed out by Professor Kendall, have the form of a reversed 3, and the region within this figure has become known generally as the Northumbrian Fault Block. Professor Marr has aptly termed the southern half of this area the “Rigid Block”. The northern half of the Northumbrian Fault Block, which will be shown to possess many characters in common with the southern half, is here called the “Aiston Block”. Its limits are defined on three sides—by the Stublick Fault on the north, the Pennine Fault on the west, and by the Stainmore depression on the south. The last thus divides the Northumbrian Fault Block into two, physiographically and structurally. The eastern boundary of the Alston Block is concealed beneath the Mesozoic rocks.

A detailed description of an important specimen of Euphoberia ferox (Salter, 1863) is given. The fossil consists of nine consecutive segments in natural association exhibiting not only dorsal structures but also some of the less-known ventral features.

The Middle Jurassic of Yorkshire consists of non-marine strata, known collectively as the Estuarine Series, and several intercalated marine bands. The non-marine beds have the characteristics of deposits formed as a delta rather than in an estuary, and are, in fact, strongly reminiscent of the Coal Measures in their general appearance. In the coast section, where they are admirable exposed, which are usually due to the presence of false bedded sediments replacing the normally parallel bedded strata. Thick wedges of sandstone replacing the Dogger, and sometimes part of the Upper Lias too, have been described by Dr. Rastall and Fox-Strangways. They are particularly noticeable when they interrupt the top seam (i.e. the Dogger) in the iron mines, where they are called “freestone baulks” by the miners. The same phenomenon is better known in the Coal Measures, where the term “washout” is used for a mass of sandstone suddenly replacing coal. Although there are several objections to the term “washout”, it is used here since it had become so well established in Coal Measures geology.

The geological succession and structure of the district are briefly summarized. Evidence of stress conditions becomes increasingly abundant as one passes from south to north towards the boundary of the Carboniferous.

The thermal alteration due to the Bodmin Moor granite is definitely delimited by tracing the outer limit of spotting in normal pelitic sediments.

Petrographical study of phyllites from outside this limit shows considerable mineralogical reconstruction in the sediments, with crystallization of white mica, chlorite and chloritoid; in some instances garnet is developed. The distribution of these types shows no relationship to the granite outcrop, but accords with the main structural features of the area.

Analogous changes are prominent in the igneous horizons, with the formation of schists of the general type of prasinite.

Within the aureole thermal effects can be traced superposed on the earlier dynamic changes.

From these lines of inquiry it is concluded that many of the changes in the phyllites, notably the formation of porphyroblastic white mica, chlorite and chloritoid, hitherto ascribed with greater or less finality to the action of the granite, are due to an earlier dynamic metamorphism.

Between the years 1869–83 the Triassic sandstone of North-East Ireland was examined and mapped by the Geological Survey under the direction of Hull. The rocks were correlated with those of similar age in Lancashire and Cheshire, the lithological characters described and the exposures noted. Later the Belfast district was resurveyed under the direction of Lamplugh, who suggested, in the Memoir published in 1904, that the Triassic sandstone should be correlated with the St. Bees sandstone rather than with that of Lancashire and Cheshire. Attention was also drawn to the probable incorrect mapping of the Trias near Belfast.

The section was visited by us in company with Dr. H. H. Thomas, of the Geological Survey, and F. A. Marr, Esq., in May, 1927.

The possibility of an unconformity at the base of the Ashgillian in North Wales seems to have suggested itself to several of those who have worked in that region. A definite verdict, however, has never been recorded, and the prevailing, if not general, view is that the Caradocian and Ashgillian are everywhere conformable.

In a paper (1) by one of us (W. F. F.) reference is made to the occurence in Midland sediments of apatite grains having dark purplish, often pleochroic, cores or nuclei. From an examination of the heavy minerals in Midland rocks ranging from Cambrian to Trias it is evident that these peculiar apatite grains occur at several horizons. Discoloured grains appear in the Cambrian quartzite and apatite of smoky tint in the Old Red Sandstone. In the Carboniferous rocks, dark-banded grains varying in tint from yellowish-brown to smoky-purple and occasionally pleochroic, occur with fair frequency. Similar grains are particularly noticeable in the Gornal Sandstone, which lies in the lower part of the Middle Coal Measures of South Staffordshire. An hexagonal cross section of apatite from this rock, with a dark core, was figured in the paper referred to above. Similar grains occur, though rarely, in the Enville and Bunter Sandstone, but increase in frequency in the lower Keuper Sandstone. The dark-colored “cores” may be sharp-edged or rather indefinite in contour, narrow or broad, and variable as regards depth of tint. Clear-cut bands or stripes of dark colour are exceptional.

Some time before the war I examined the profiles, or longitudinal sections, of several rivers, with the object of ascertaining whether they tended towards any particular curve. The method of examination was similar to that employed by Professor O. T. Jones in his interesting paper on “The Upper Towy Drainage System”, but the data were obtained from maps and were not so exact as his. Some rivers showed a very close approximation to a catenary for the greater part of their course, but this was not the case with all. My final conclusion was that there is no general curve towards which all river-profiles tend the form is influenced by the rate at which the volume of the river increases downwards. No sufficient data, however, were available in the case of any river for the exact application of a general theory which was in my mind, and such approximations as were possible were too rough to be of any real value.