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IV.—The Lower Pliensbachian— ‘Carixian’—of Charmouth

  • W. D. Lang
Extract

The Green Ammonite Beds of the Lias (called also the Wear Cliff Beds in the latest Survey publication on Lyme Regis) include the clays with occasional limestones that lie between the Belemnite Stone below and the lowest of the Three Tiers above. The lowest Tier contains ammonites of the margaritatus group, and the Belemnite Stone caps the top beds of the Belemnite Marls that may be placed in the ibex-valdani zone. So the Green Ammonite Beds may be said to constitute the upper part of such of the Pliensbachian or Charmouthian as lies below the Domerian. Buekman has applied the term ‘Charmouthian’ to this lower portion, thus restricting the term to a part only of what it originally included. I have already advocated the propriety of applying the term Charmouthian strictly with its original connotation, and would call those zones of it that lie below the Domerian,—Bonarelli's ‘Charmoutiano inferiore’—which certainly need an inclusive name, Carixian. The fullest published accounts of the Green Ammonite Beds are those in the Survey Memoirs, and may be summarized as follows: They extend from Black Ven on the west to Seatown on the east; traces only appear on Black Ven; the complete series occurs on Stonebarrow, though there “only the lower portion is well-exposed”; their thickness is about 100 feet, though variable, and as much as 125 feet to the east of Golden Cap; they consist of marly clays with ‘ferruginous bands’ and nodular limestones.

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page 401 note 1 Woodward, & Ussher, , The Geology of the Country near Sidmouth and Lyme Regis (Mem. Geol. Surv. Eng. and Wales), 1911, 2nd ed., p. 31.

page 401 note 2 Throughout this paper the phrase “ammonites of the — group” is used, rather than the specific name of the ammonite, implying that several, presumably related forms are included under one designation.

page 401 note 3 On the evidence of Acanthopleuroceras ellipticum (James Sowerby), a form that comes very near to A. valdani. Mr. S. S. Buekman kindly identified this form for me.

page 401 note 4 Bonarelli, , Atti della R. Accad. d. Scienze di Torino, vol. xxx, pp. 84–5, 1894.

page 401 note 5 Buckman, , Yorkshire Type Ammonites, pt. ii, p. xvi, 1910.

page 401 note 6 Lang, , Geol. Mag., Dec. V, Vol. IX, p. 284, 1912.

page 401 note 7 Charmouth, the Carixa of Ravennas” (Roberts, , The History of Lyme Regis, Dorset, 1823, p. 220). The derivation seems obvious — Char-isca, ‘Char-river.’

page 402 note 1 Woodward, & Ussher, , op. cit., 1911; and op. cit., 1906, 1st ed.; Woodward, H.B., The Lias of England and Wales (Mem. Geol. Surv. United Kingdom), 1893, p. 68.

page 402 note 2 See Woodward, H. B., op. cit., 1893, p. 52.

page 404 note 1 Described, Lang, , Geol. Mag., Dec. V, Vol. I, pp. 125, 126, 1904. It was visited by the Geologists' Association in 1906, see Proc. Geol. Assoc, vol.xix, pt. ix, p. 323.

page 404 note 2 The great undercliff on Stonebarrow, called ‘Cain's Folly’ on the six-inch Ordnance Survey map. I use the more familiar local name.

page 404 note 3 The Survey, following Day (Quart. Journ. Geol. Soc, vol. xix, p. 282, 1863), give a downthrow of only 40 feet (see Woodward, H. B., op. cit., 1911, p. 30); but considering that at this point the Bed Band is reckoned at 45 feet above the Belemnite Stone, it must be about 95 feet above the beach on the west side of the fault, while it is beneath the beach 5 or 6 feet below the cliff-base on the east side of the fault; hence 100 feet is a fair minimum estimate of the downthrow. It is possible that there is a second fault a few yards further east, sharing the 100 ft. downthrow with the obvious fault, but this has not yet been definitely ascertained, and at any rate does not affect the present question.

page 407 note 1 See Geol. Mag., Dec. V, Vol. IX, p. 285, 1912.

page 407 note 2 See Geol. Mag., loc. cit., 1912.

page 407 note 3 Lang, , Geol. Mag., Dec. V, Vol. IV, p. 150, 1907.

page 408 note 1 This concerns the general shape of the Cretaceous base-line in this district, see Jukes-Browne, , Proc. Dorset Nat. Hist. Club, vol. xviii, p. 176, 1897; and Geol. Mag., Dec. IV, Vol. V, p. 164, 1898.

page 408 note 2 The most detailed account is in Woodward, H. B., op. cit., 1893, p. 69.

page 408 note 3 The Stonebarrow or Belemnite Beds of the Survey Memoirs.

page 408 note 4 Woodward, H. B., op. cit., 1893, p. 67.

page 408 note 5 Woodward, H. B., op. cit., 1893, p. 68.

page 410 note 1 Woodward, & Ussher, , op. cit., 1911, p. 30.

page 410 note 2 The Survey follow Day in calling these indurated marls, limestones; see Day, Quart. Journ. Geol. Soc., vol. xix, p. 281, 1863. On p. 280, however, Day speaks of “semi-indurated limestone”, which is a far less misleading description.

page 411 note 1 A. Escher von der Linth, “Geol. Bemerkungen u. d. nördlīche Vorarlberg und einige angrenzenden Gegenden,” 1853, p. 1, pl. i, figs. 1–5. See also Ooster, W., in Fischer-Ooster, C. von, “ProtozoeHelvetica,” vol. i, pt. ii, pl. xii, figs. 1–5, pp. 36, 37, 1869. I am indebted to my colleague, Mr. R. B. Newton, for kindly identifying this form.

page 411 note 2 The following additional note was added by Mr. Buckman, S. S., who kindly identified this form: “?= young of d'Orbigny's large figure of Uptonia regnardi,” d'Orbigny, 1842, Pal. Franç. Terr. Jur., p. 257, pl. lxxii, fig. 1.

page 411 note 3 Mr. S. S. Buckman has kindly examined this form and identified it with Acanthopleuroceras ellipticum (James Sowerby), “very near to A. valdani.”

page 412 note 1 Woodward, H. B., op. cit. 1893, p. 68.

page 412 note 2 Woodward, H. B., op. cit. 1893, p. 65, “Am. Stellaris in nodules.”

page 412 note 3 See ante, pp. 401–2.

page 412 note 4 Woodward, H. B., op. cit. 1893, p. 60.

page 412 note 5 Woodward, H. B., op. cit. 1893, p. 52.

page 412 note 6 Woodward, H. B., op. cit. 1893, p. 66.

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