Abstract
LONDON. Geological Society, December 7.—Mr. R. D. Old-ham, president, in the chair.—S. S. Buckman: Jurassic chronology; II., Preliminary studies. Certain Jurassic strata near Eype's Mouth (Dorset): the junction-bed of Watton Cliff and associated rocks. A detailed section is recorded of a white lithographic bed in Watton Cliff which shows faunal inversion. The dating of this bed is discussed, and a theory of stratal repetition and coalescence is discussed. Its main date is taken to be Yeovilian, Hammatoceras hemera. The white lithographic bed of Burton Brad-stock is cited as evidence of stratal repetition, and a theory as to its deposition and partial destruction is put forward. Both beds are cited as evidence of Alpenkalk conditions prevailing in western Europe at two well-separated Jurassic dates, both of them earlier than the times of Alpenkalk deposits in central and eastern Europe. A new species of rhyncho-nellid from a deposit at Thorncombe Beacon is described.—J. Stansfield: Banded precipitates of vivianite in a Saskatchewan fireclay. The pale grey Tertiary fireclay worked for firebricks contains bluish-black patches, the central portions of which are deeply coloured and usually surrounded by a uniformly stained area or by several concentric stained layers of varying tint. The colour is due to an amorphous variety of vivianite, formed presumably by precipitation brought about by iron-solutions reacting on solutions of phosphates of organic origin, such solutions being brought together by diffusion through the colloidal clay. The spacing of the vivianite-bands is irregular, and appears to follow no known law.
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Societies and Academies. Nature 108, 589–591 (1921). https://doi.org/10.1038/108589b0
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DOI: https://doi.org/10.1038/108589b0