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On the Age of Certain Species of Trigonia from the Jurassic Rocks of Kachh (Cutch)

Published online by Cambridge University Press:  01 May 2009

L. F. Spath
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Extract

One of the problems left unsolved in my “Revision of the Jurassic Cephalopod Fauna of Kachh” consisted of the determination of the exact age of certain Jurassic beds that had yielded (in addition to ammonites) species of Trigonia. Among these, T. smeei J. de C. Sowerby is of unusual, general interest; and, as readers of the Geological Magazine may remember, this species has been the subject of much controversy. It was one of the species whose “morphological position, viewed from the evolutionary standpoint”, caused them to be described as Cretaceous. Thanks to the continued researches of Mr. J. H. Smith, of Bhuj, who has been good enough to send me new collections from various critical sections in Kachh, I am now in a position to add to the evidence for a Jurassic age of a number of these species of Trigonia. If it be asked why, in a work on cephalopods, I have gone out of my way to express scepticism regarding the use of species of Trigonia for correlation, I can only say that this genus happened to be represented among the ammonite material sent to me. There is no reason, so far as I can see, why Trigonia should not be quite as useful for zonal purposes as ammonites. I have been equally sceptical about Stolley’s work on belemnites. But in either case I will leave the results to speak for themselves. It seems to me that if Upper Oxfordian species like Trigonia smeei and such allies as T. tenuis, T. tra-peziformis, T. remota Kitchin, not to mention the associated Astarte, Gervillia, Cucullaea, Exogyra, etc., could be claimed to be of Cretaceous age by one of the most eminent authorities, then it is time to remind the general palaeontologist again of what workers on ammonites have realized long ago.

Type
Original Articles
Information
Geological Magazine , Volume 72 , Issue 4 , April 1935 , pp. 184 - 189
Copyright
Copyright © Cambridge University Press 1935

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References

page 184 note 1 “Memoirs of the Geological Survey of India,” Palaeontologia Indica, New Series, ix, No. 2, pts. i–vi, 1927–1933.Google Scholar

page 185 note 1 Kitchin, F. L., “On the Age of the Upper and Middle Deinosaur-Deposits at Tendaguru, Tanganyika Territory,” Geol. Mag., 1929, LXVI, 208. See also F. L. Kitchin, “The So-called Malone Jurassic Formation in Texas,” Geol. Mag., 1926, LXIII, 468.Google Scholar

page 185 note 2 Spath, , loc. cit. (Pal. Indica), pt. v (1931), explanation to pi. cxvii; pt. vi (1933), p. 660.Google Scholar

page 185 note 3 “Memoir on the Geology of Kutch,” Mem. Geol. Survey India, 1872, ix, 12Google Scholar

page 185 note 4 Spath, , loc. cit. (Pal. Indica), pt. iv, 542.Google Scholar

page 186 note 1 “Geologie der frankischen Alb zwischen Eichstätt und Neuburg a. D” Geogn. Jahresh., xxvii (1914), 1915, 93, pl. iv, fig. 1.Google Scholar

page 186 note 2 The Geological Survey spelling of Kimmeridge is adhered to; I consider that geologists have no right to choose their own spelling in the case of a place actually in existence and possessing a Post Office.

page 186 note 3 Consisting of: Perisphinctes jelskii Siemiradzki, P. aff. inconstans (Spath), P. aff. orientalis Siemiradzki, Prososphinctes virguloides (Waagen), P. sp. nov. aff. virguloides (Waagen), Discosphincles aff. virgulatus (Quenstedt), Torquatisphinctes cf. torquatus (J. de C. Sowerby), Epimayaites sp. ind.

page 187 note 1 The new Jurun assemblage is as follows: Torquatisphinctes alterneplicatus {Waagen), also var. maculata Spath and an evolute variety; T. jurunensis Spath, T. similis Spath, T. sp. ind., T. sp. nov. (depressed, transitional to Pachyplanulites irregularis), Planites consociatiformis (Simionescu), P. aff. breviceps (Quenstedt), Metahaploceras pascoei Spath, M. aff. kobyi (Choffat), M. sp. (pseudoflexuosum Choffat non Favre), Holcophylloceras mesolcum (Dietrich), Aspidoceras asymmetricum, Spath, A. aff. bispinosum (Zieten), Hibolites spp. (hastatus-claviger group).

page 187 note 2 Kitchin, , “Memoirs Geol. Survey India,” Pal. Indica, Ser. ix, Jurassic Fauna of Kutch. III, 2, Lamellibranehiata. No. 1. Genus Trigonia, 1903, p. 113.Google Scholar

page 188 note 1 “A Contribution to the Stratigraphy of Cuteh,” Quart. Journ. Geol., Mining, Metall. Soc. India, 1932, iv, No. 4, 171.Google Scholar

page 188 note 2 In litt., 24th July, 1929. See Spath, , Monograph of the Amnwnoidea of the Gault” Pal. Soc, vol. i, 1930, pp. iii, iv.Google Scholar

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page 189 note 2 “Mem. Geol. Surv. India,” Pal. Indica, N.S., xx, No. 5 (1935).Google Scholar

page 189 note 3 Spath, , loc. cit. (Pal. Indica), pt. vi, 1933, 826–9.Google Scholar