CORRELATION AND FACIES OF THE UPPER AND MIDDLE OOLITES IN ENGLAND AND NORTH-WEST FRANCE

Abstract

(Read November 18th, 1914.) The Jurassic, probably better than any other System, emphasizes the fact of a gradual transition of one series into another by means of passage beds, represented locally by unconformities,* and in spite of numerous local facies, the general sequence may be readily followed. The beds dealt with in this paper comprise a well-marked group of clays, sandstones and limestones, the “Tripartite Series” of Phillips,† commencing with the Cornbrash at the base and terminating with the Purbeck Beds at the top. These beds have been very fully dealt with, not only in the Memoirs of the Geological Survey, but also in numerous individual papers by Messrs. Blake, Hudleston and, more recently, Morley Davies.‡ In spite, however, of the attention that these beds have most deservedly received, there appears to be no readily accessible paper in which their general correlation can be found§. At Prof. Kendall’s suggestion, therefore, I am venturing to attempt to supply this want. Perhaps the most remarkable feature of the whole series is the inclusion at various horizons of arenaceous and calcareous facies in what is as a general rule an argillaceous series of beds. As has been pointed out by Blake, Hudleston and others, these beds are to be regarded as purely accidental, and the fauna is in every case transitional, the apparent sharp palaeontological breaks being due to environment rather than to an actual change in a fauna by the extinction of a previous one. We thus find, as we should expect, ...