Abstract
LONDON. Geological Society, April 4.—G. W. Tyrrell: The analcite-syenites and associated rocks of Ayrshire. These rocks occur in differentiated intrusions along with analcite-olivine-dolerites or crinanites, as stratiform bands, schlieren, and veins. The principal occurrence is at Howford Bridge, Mauchline, where analcite-syenite forms a considerable part of the sill. In the remaining three described occurrences (Dippol Burn, Trabboch Burn, and Prestwick) the analcitesyenite is restricted to schlieren and veins. They all belong to the widespread suite of analcite-bearing igneous rocks of late-Carboniferous and Permian age in the west of Scotland. The most noteworthy mineralogical feature is the abundant occurrence of analcite, thomsonite, natrolite, and prehnite, which must be regarded as late primary crystallisations from the magma. A hypothesis for the development of schlieren and veins in the sills by the effects of the varying incidence of the pressure due to the superincumbent column of rock, upon a crystal mesh filled with interstitial liquid, is framed. The liquid is believed to be progressively driven towards the centre of the sill, and also laterally towards those places where the pressure is compensated in various ways, so that free contraction of the crystallising mass can take place.“J. Parkinson: A note on the Pleistocene history of western Buchivacoa (Venezuela). The area consists of alternating estuarine or freshwater false-bedded sandstones, and sandy clays, folded along east-north-easterly axes in many places. Burdigalian and Aquitanian fossils occur in the eroded centres of the folds. There is an unconformity between the Miocene and the overlying strata, which appear to be of Lower or Middle Pliocene age. The Tertiary deposits are covered by Pleistocene pebblebeds. The latter are probably an old sea-beach. Subsequent elevation during a pluvial period allowed of a ‘creep’ of the pebbles northwards. Redeposition in successive stages was effected by eastwardflowing rivers of the Indus type. Since Pliocene times, an elevation of about 1000 feet has taken place along the southern edge of the district.—A. Tindell Hopwood: Gyrinodon quassus, a new genus and species of toxodont from western Buchivacoa (Venezuela): with a note on the reptilian remains by W. E. Swinton. Gyrinodon differs from Toxodon in its more primitive dentition, and in the characters of the skull-cap. It differs from Alitoxodon in the characters of the mandibular symphysis. This is the northernmost locality for toxodonts hitherto recorded in South America. Apparently the toxodonts followed a northward dispersal.
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Societies and Academies. Nature 121, 693–695 (1928). https://doi.org/10.1038/121693a0
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DOI: https://doi.org/10.1038/121693a0