The Northumbrian Fault-block, forming the central part of the Pennine Chain, is a region of gently tilted Carboniferous sediments, bounded on the north, west, and south by major faultlines. It is divided naturally into two structurally complementary areas, symmetrically disposed to the north and south of the syncline of Stainmore. The present paper is concerned exclusively with the northern area, named by F. M. Trotter and S. E. Hollingworth the “Alston Block” (1928) and by H. G. A. Hickling the “Cross Fell Block” (1930). The first-named authors, who have recently completed a revision of the Geological Survey sheet covering the north-west corner of the block, have discussed in detail the structure of that district and have described the broad outlines of the tectonic history of the block (1928, 1932).

Modern detailed stratigraphical studies have demonstrated very clearly the long and involved tectonic history of the majority of the main structural units of England. It has been proved that, in certain areas, the thickness and the lithology of the sediments were partly determined by repeated pene-contemporaneous folding along definite axes, and thus it has been possible to trace the gradual growth of some of the main fold lines of the country. The Weald is typical of these areas, whose structure, at first sight simple enough, reveals on closer study much complexity of the minor folding and faulting and also gives evidence of long continued movement along certain lines; movement contemporaneous with the deposition of beds which were involved in the final crescendo of tectonic activity.

The following is a description of the conglomerates which crop out at Allt Goch and Mathrafal-ffrîdd near Meifod (Montgomeryshire) and which were examined on the suggestion of Professor W. B. R. King. Allt Goch is about 4 miles north of Mathrafal-ffrîdd, and the two localities lie on opposite flanks of the anticlinal structure which passes through Pont Robert and which, brings up Ashgillian and Caradocian rocks. The conglomerates themselves are at, or near, the base of the Valentian. At other places in the neighbourhood the basal member of the Silurian consists of coarse deposits (sandstones, etc.), but “they very probably do not represent the lowest zones that are found in Central Wales” (I).

In his posthumous paper on the geology of the Island of Raasay H. B. Woodward (1) remarks: “On the fore-shore south of Oskaig Point, the modern beach is cemented into a conglomerate.” The unique mineralogical composition of this conglomerate, which has been collected in the course of a study of the Tertiary igneous rocks of Raasay and neighbouring islands, warrants the following note.

The records of fossil fishes in the Denbighshire Coalfield appear even more scanty than those of the molluscs, and one of the first references1 is to a fish-bed in the roof of the “ Queen Coal ” at Llay Hall Colliery in the north of Denbighshire. This coal is 300–400 feet from the bottom of the Middle Coal Measures, and is known as the “ Premier ” in Flintshire, and in South Denbighshire as the “ Wall and Bench ”. Throughout Denbighshire it is the lowest generally worked seam of the productive measures, as the coals below it are few and, in any case, too thin for profitable operation, except when in association with pottery clay.