Remarks upon the relations and grouping of the Permian and Triassic rocks / by Horace B. Woodward.

  • Woodward, Horace B. (Horace Bolingbroke), 1848-1914.
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: Remarks upon the relations and grouping of the Permian and Triassic rocks / by Horace B. Woodward. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    able principally by colour, but also by other mineral characters.” Further on Mr. Hull speaks of it, as “ this, to all appearance, un- conforinable overlap of the lower division of the Trias.” ^ In Shropshire, Mr. Hull remarks that “ there is some uncertainty as to the exact line of demarcation between the Bunter and Keuper series, as the uppermost beds of the former are sometimes suf- ficiently hard for building purposes.”^ It is unnecessary to enter further into a discussion of the relations of the Bunter and Keuper formations, for these quotations will be sufficient to indicate the unsatisfactory evidence of any considerable break having occurred between the subdivisions of the Triassic rocks in England, to warrant the notion that “the close of the Bunter Sandstone period in England was accompanied by a general eleva- tion of the whole of the Triassic area, in which condition it remained throughout the period of the Muschelkalk.” ® In the south-west of England, or in the country that lies between Bristol and Exmouth, there is a considerable development of the New Bed rocks, and these have been generally included in the Trias.* In the smaller maps two divisions have been made, namely, 1. New Bed Marl and Dolomitic Conglomerate. 2. New Bed Sandstone and Conglomerate, as in Greenough’s Geological Map of England and AVales. Or 1. New Bed or Keuper Marl and Sandstone. 2. New Bed or Bunter Sandstone, as in Bamsay’s Geological Map of England and Wales. In the published Geological Survey Maps, two divisions are like- wise made, in South Devon, of New Bed Marl and Sandstone;® the latter including the pebble-beds of Budleigh Salterton and the breccias of Teignmouth. The Dolomitic Conglomerates of Mendip and those of West Somerset were, however, in places coloured distinctly. Such being the case, there must consequently be some confusion in regard to the classification of these Triassic rocks, and more par- ticularly when no recognized unconformity has been observed to justify the distinctive terms of Bunter and Keuper. Turning our attention to the coast-sections between Seaton and Exmouth,® we find a very clearly developed series. A little east of Seaton, we meet with the lower Bhaetic marls, and thence trace their ^ Op. cit. pp. 86, 87. ® Idem. p. 64. ® Hull, op. cit. p. 106. * The name Permian has sometimes crept in through a misunderstanding of the Dolomitic (or Magnesian) Conglomerate. ® These Maps include Sheets 19, 20, 21, and 22. The Sandstone is not designated as Bunter, and the boundary between it and the New Bed Marl is not engraved in Sheets 21 and 22. The whole area has been undergoing revision, and the new edition, of Sheet 19 is now published. ® This coast-line has been described and diagrams of the sections drawn by De la Beche, Trans. Geol. Soc. 2nd series, vol. i. p. 40, plate viii. (Bridport to Sidmouth); Buckland, Idem. p. 95, Plate xiv. (Portland to Lyme Regis, and Branscombe to Sidmouth); Whitaker, Quart. Journ. Geol. Soc. vol. xxv. p. 152 (Dowlands Landslip to Babbacombe Bay). See also Pengelly, Trans. Plymouth Inst, for 1862-65; Trans. Devon. Assoc, for 1863. My notes on the coast-section (which, however, add nothing to what has been written before) were made in company with my colleague, Mr. W. A. E. Ussher. He has done the greater part of the re-survey