Abstract
LONDON. Geological Society, May 12.—Prof. W. J. Sollas, F.R.S., president, and afterwards Dr. J. J. H. Teall, F.R.S., vicepresident, in the chair.—The Hartfell-Valentian succession around Plynlimon and Pont Erwyd (North Cardiganshire): O. T. Jones. The stratigraphical succession and the geological structure of an area lying in the hilly district east of Aberystwyth are dealt with. The rocks within the district are divided into three stages, which are further subdivided into groups and zones. The Plynlimon stage is developed in the northern part of the district, the Pont Erwyd stage along the two valleys of the Rheidol and the Castell, while the Ystwyth stage is developed on the plateau-like tract extending from the Castell Valley to the Ystwyth Valley. The palæontological evidence is in entire accord with the stratigraphical evidence. Three types of structure are dealt with, (1) folding, (2) strike-faulting, and (3) normal faulting, but the first is predominant. Evidence is given for assigning to the “Aberystwyth Grits” of earlier observers a position much higher in the geological sequence than has hitherto been attributed to them. The paper concludes with a tabular list of fossils, correlation tables, and a description of two species of graptolites of zonal importance.—The geology of the neighbourhood of Seaford (Sussex): J. V. Elsden. This paper deals with a portion of the South Downs lying between Eastbourne and Newhaven. The inland outcrops of the uppermost zones of the Chalk are mapped. On the east of the Cuckmere River, the beds examined are found to be nearly horizontal. On the west side they are bent into a sharp uniclinal fold, striking east and west. Seaford Head represents a remnant of this fold. The low ground between Seaford and Chyngton occupies the trough of the fold. The complete disappearance of the fold on crossing the Cuckmere cannot be satisfactorily explained by the normal process of dying-out. It is suggested that a transverse fault may exist beneath the alluvium of that river. The fault, if it exists, seems to die away northwards, since no trace of it has been detected higher up the valley. The relation of the Seaford fold to the main flexures of the south coast is considered. Certain existing physlographical features are ascribed to the influence of this flexure, which facilitated the retention of the Eocene cover in the synclinal hollow thus formed. A brief comparison is made between the fossils of the inland exposures and those of the cliff-sectipn, the most notable difference being the evidence in the former of a Conulus band at the top of the zone of Micraster cor-anguinum.
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Societies and Academies . Nature 80, 419–420 (1909). https://doi.org/10.1038/080419a0
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DOI: https://doi.org/10.1038/080419a0