The Whin Sill of this district has the form of a series of sills at different stratigraphical levels. Minor scarps at right angles to the main trend of the sill are explained by intrusion of offshoots, from its upper surface, along low angled fractures in the superincumbent strata. An intrusion mechanism is suggested to account for the presence of the Oxford Limestone both above and below the Whin Sill.

Large ignimbrite dykes continuous with an overlying sheet of rhyolitic ignimbrite have been found at two localities in the centrally-subsided block of the Sabaloka cauldron. There is good evidence that these dykes fed ash-flow eruptions. Other possible feeder vents occur along the marginal fracture zone of the cauldron but evidence for the origin of some of these structures is ambiguous. Ignimbrites within the dyke-shaped feeders contain a very strong eutaxitic foliation oriented parallel to the contacts and this feature is thought to result from inwardly-directed pressures exerted by the dyke walls during a collapse which followed eruption of the ash-flows. Vents of this type are believed to originate by permissive intrusion through the roof of a shallow-seated magma chamber, in contrast to forcefully injected diatreme vents. A broad genetic classification of these bodies is suggested, based on their mode of emplacement.

THE late Dr. Vaughan, in 1905, established the age of the sand-stone lying above the Whitehead Limestone of the Forest of Dean as of upper Seminula age, and not, as had been supposed, as the equivalent of the Millstone Grit. Later, in 1912, Dr. T. F. Sibly described the sandstone as “ composed very largely of pure quartz sandstones, often coarse-grained and friable. Conspicuous bands of quartz conglomerate occur: some clays and shales are intercalated, with the sandstones: and some haematite deposits are developed ”. The same author described the structure of the Forest of Dean coalfield and noted the perfectconformity of the Dry brook Sandstone on the Whitehead Limestone and the overstep of theCoal-measures. The latest description of the sandstone, and the one which is most complete, is given by Dr. Sibly in his work on the ironstone of the Forest of Dean. His description reads “ Red, white, and mottled red and white sandstones compose the bulk of the formation. The rocks are mainly friable, but compact and even quartzitic rocks occur. In the north-east seams of quartz conglomerate are numerous. In the south-west bands of gritty limestone and dolomite develop ”.

I regret that this short but important communication was too late for insertion in the December number of the Geological Magazine, as it was intended to announce the discovery of no less than four, if not five, new Genera of Amphibian Labyrinthodont Reptiles from the true Coal-beds of Jarrow Colliery, Kilkenny, Ireland.