Societies and Academies

Abstract

LONDON. Geological Society, November 23.—Prof. W. W. Watts, F.R.S., president, in the chair.—Dr. W. F. Hume: The effects of secular oscillation in Egypt during the Eocene and Cretaceous periods. There is evidence of the gradual advance of the Cretaceous sea from north or north-east over Egypt during Upper Cretaceous times. Four stages in this advance are indicated by the distribution of the Cretaceous deposits. The four phases are:—(a) A north Egyptian type, in which the Nubian Sandstone entirely underlies fossiliferous beds of Cenomanian age. This extends across Egypt from Sinai to Baharia Oasis, (b) A Wadi-Qena type, developed near the head of the valley of that name, characterised by the alternation of Nubian Sandstone with fossiliferous Cretaceous beds. (c) A central Egyptian or Hammama type, in which the Nubian Sandstone forms the greater portion of the Cretaceous series, only the Danian and Campanian beds being fossiliferous limestones or shales. The Campanian beds are characterised by the presence of phosphatic fish-beds. (d) A south Egyptian type has resemblances to the central I Egyptian, but in the Campanian the phosphatic beds are inconspicuous. As regards the transition from the Cretaceous to the Eocene, the existence of two types of strata at the base of the Eocene is noted: the first, the Luxor type, being fossiliferous, and developed in the Western Desert; the second, or Qena type, being unfossiliferous, and composed of white limestone similar to the Danian white limestone below them, but structurally different. These variations may be due to fold-effects produced while the land was gaining on the sea at the beginning of Eocene times, the Qena limestones being remade Cretaceous material. Whereas in southern Egypt Lower Eocene strata directly overlie the Danian strata, in northern Egypt unconformities exist between the Middle Eocene and the Cretaceous beds. The palæontological differences between the Cretaceous and the Eocene are recorded, the principal feature being the sudden incoming of the foraminifera Nummulites and Operculina. The distribution, zonation, and variation of the Eocene series are considered. The apparent uniformity of the fossiliferous Lower Eocene strata wherever developed is noted. The lack of uniformity in the Middle Eocene strata. The nature of the Eocene beds between Baharia Oasis and the depressions of Moela and the Fayum are described, zoned, and compared with the Middle Eocene in other parts of Egypt. The influence of the gain of land over sea is traced through the Upper Moqattam beds. The Cretaceous period in Egypt is marked by the gradual gain of sea over land; during the Eocene land appears to have been steadily gaining on the sea, probably accompanied by gentle fold-movements, which account for the minor differences in the nature of the Eocene deposits.—A. R. Norwood: The origin of the British Trias. During the Triassic period in Britain, deposition, it is maintained, was brought about solely by the action of water, and the British Trias is a delta-system, for during Carboniferous, Permian, and Triassic times deposition was mainly in the same area. There is a gradation from the Bunter to the Rhætic. The Bunter is known to be of fluviatile origin, and there is a continuity from Lower to Upper Trias, with an unconformity due to the new mode of formation and change in sedimentation. Oscillation and overlapping are admittedly due to aqueous agency. The Triassic outcrop and the delta-area of the river Mississippi are closely similar. Coloration is original, from below upwards, and not coincident with bedding. The thickness of the Bunter is an argument for a subsiding area. The ferruginous types in the Carboniferous, Permian, and Trias are alike due to delta conditions. The Trias is horizontal now, as originally, away from any ancient hills which it covers. It is only the skerries that are rippled. Screes occur mainly to the south-west of submerged hills. Sandstones thin out eastward, marls westward, and the skerries are on the hills. Rock-salt and gvpsum are also horizontal and continuous in a linear direction. The Keuper gradually merges into the Rhætic phase, and the latter into the Lias. Since the Bunter sediments came from the north-west into the Midlands, so probably did the Upper Trias. Local metamorphic and volcanic rocks may have provided some of the heavier minerals, but, as a whole, their source was more distant. The flora and fauna can be grouped in provinces around the delta-head of the Trias. These considerations point to an aqueous mode of sedimentation in a moist and equable climate.