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II.—Notes on the Relations of the Rhætic Beds to the Lower Lias and Keuper Formations in Somersetshire1
Published online by Cambridge University Press: 01 May 2009
Extract
It would at first sight seem superfluous that anything more should be written upon the relations of the Rhætic Beds in England, for during the past twelve years they have received so much attention—the principal sections have been described, and the beds have been well and successfully searched for fossils. But whilst there has been no lack of petrological and palæontological evidence,—and we ought to be very thankful to railway companies in the western counties for opening up so many fine sections,—still it is somewhat astonishing to remark, there has been and there still appears to be a considerable diversity of opinion on the subject of the relations of the beds. Some authorities have placed them with the Lias, others with the Trias; some regard them as quite an independent formation, others as passage-beds belonging as much to the one as to the other.
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Footnotes
1
This paper is published by permission of the Director-General of the Geological Survey.
References
page 196 note 2 Quart. Journ. Geol. Soc., vol. xxvii. p. 189.
page 196 note 3 Quart. Journ. Geol. Soc., vol. xvii., p. 483.
page 196 note 4 H. W. Bristow, Report Brit. Assoc. for 1864; Geol. Mag., Vol. I., p 236. See also W. B. Dawkins, Quart. Journ. Geol. Soc., vol. xx., p. 396; Geol. Mag., Vol. I., p. 257; Vol. II., p. 481.
page 197 note 1 “Sun-bed” is the term applied by quarry-men in the neighbourhoods of Bath and Radstock to the top bed of the White Lias. It is a hard cream-coloured or bluish limestone with a conchoidal fracture. The term “Jew-stone” is applied to the same bed near Wedmore and along the Polden Hills.
page 197 note 2 We must refrain from details, as these will appear in a Geological Survey Memoir on the district, now in course of preparation.
page 198 note 1 Quart. Journ. Geol. Soc., vol. xxiii., p. 459, etc.
page 198 note 2 Quart. Journ. Geol. Soc., vol. xvii., p. 487; vol. xxiii., p. 471.
page 198 note 3 Ammonites planorbis occurs at Keynsham, and we have noticed it in the cutting near Bitton Station on the Midland Railway. We have also obtained it in the cherty beds of the Lias at Harptree Hill.
page 199 note 1 De la Beche's Geological Report on Cornwall, Devon and West Somerset, p. 232.
page 199 note 2 Quart. Journ. Geol. Soc., vol. xxiii., p. 468.
page 199 note 3 I am inclined to think that the veins were formed after the beds were consolidated, the striæ being always at right angles to the walls of the same, whereas the nodules may have been formed by segregation or otherwise when the beds were unconsolidated, and perhaps shortly after their deposition.—J.H.B.
page 199 note 4 Quart. Journ. Geol. Soc., vol. xxvii., p. 197.
page 200 note 1 Amongst whom Moore, Quart. Journ. Geol. Soc., vol. xxiii., p. 496.
page 200 note 2 Tate, Census of the Marine Invertebrate Fauna of the Lias, Geol. Mag., Vol. VIII., p. 4.
page 200 note 3 A short Introduction to the Study of Geology, 1817, p. 21.
page 200 note 4 Geology of England and Wales, p. 264.
page 201 note 1 Observations on the Earths, Rocks, Stones, and Minerals about Bristol, etc., 1754, p. 163.
page 201 note 2 Quart. Journ. Geol. Soc., vol. xxvii., p. 189. See also Memoir of Edward Forbes, by Wilson and Geikie, p. 418.
page 201 note 3 At Nempnet, near Chew Stoke, I mapped, in 1867, some beds of Conglomerate as of Rhætic age.—H. B. W.
page 201 note 4 The idea was first suggested to us in 1868 by Mr. Gibbs, late of the Geological Survey. It is also held by Mr. Moore, in his paper on the Geology of the Mendips, Proc. Somerset Arch. and Nat. Hist. Soc., vol. xv.
page 201 note 5 Mem. Geol; Survey, vol. i., p. 272.
page 202 note 1 Proc. Cotteswold Nat. Field Club for 1864, Vol. iii., p. 220.
page 202 note 2 I would urge that a uniform system be adopted in our classification of strata. By placing the Rhætic beds as a separate period, we give the beds an importance which they certainly do not possess in this country; and therefore it seems better to include them in the Trias, mainly as a matter of convenience, as such an arrangement is now adopted by the highest anthorities. Vide Jukes and Geikie, Manual of Geology. Account of Rhætic Beds, p. 613, by H. W. Bristow. Hull, Memoir on the Triassic and Permian Rocks of the Midland Counties of England. Phillips, Geology of Oxford and the Valley of the Thames, p. 101.—H. B. W.