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II.—On the Organic Origin of the Chert in the Carboniferous Limestone Series of Ireland, and its Similarity to that in the Corresponding Strata in North Wales and Yorkshire

Published online by Cambridge University Press:  01 May 2009

George Jennings Hinde
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Extract

The first references in any detail to the nature of the Chert in Carboniferous rocks appeared in 1878, when Messrs. Hull and Hardman published a joint paper on the subject, treating more particularly of the Chert in the Upper Carboniferous Limestone of Ireland. Prof. Hull gave a general description of the distribution and mode of occurrence of the Chert, and a detailed notice of its microscopic structure, as shown in fifteen thin sections of the rock from various localities in Ireland. Prof. Hull gave a general description of the distribution and mode of occurrence of the Chert, and a detailed notice of its microscopic structure, as shown in fifteen thin sections of the rock from various localities in Ireland. The author reached the conclusion that the Chert is essentially a pseudomorphic rock, consisting of gelatinous silica replacing limestone of organic origin, chiefly foraminiferal, crinoidal, and coralline; the replacement was believed to have taken place before the shales overlying it were deposited, whilst the limestone was in a more or less plastic condition, admitting the fine percolation of water holding silica in solution. The sea was believed to have been largely charged with silica in solution, and the chemical process was accelerated by the warm surface waters of a shallow sea. The origin of the Chert from the siliceous skeletons of Biatomaceas, Polycystinas, and the spicules of sponges is distinctly denied, and it is affirmed that it can only be considered as a secondary product due to the replacement of lime-carbonate by silica.

Type
Original Articles
Information
Geological Magazine , Volume 4 , Issue 10 , October 1887 , pp. 435 - 446
Copyright
Copyright © Cambridge University Press 1887

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References

page 435 note 2 Scientific Transactions of the Royal Dublin Society, vol. i. n.s. 1878, pp. 71–94, pl. iii.Google Scholar

page 436 note 1 Bulletin de l'Académie Royale de Belgique, 2 s. t. 46, pp. 471–498, pl. i.Google Scholar

page 436 note 2 Op. cit. p. 498.Google Scholar

page 436 note 3 Ann. and Mag. Nat. Hist. vol. vii. (1881) p. 141.Google Scholar

page 437 note 1 Ann. and Mag. Nat. Hist. s. 5, vol. vi. (1880) p. 213.Google Scholar

page 437 note 2 On Beds of Sponge-Remains in the Lower and Upper Greensand of the South of England, Phil. Trans, pt. ii. 1885, pp. 405–453, pls. 40–45.Google Scholar

page 437 note 3 Proc. Royal Soc. vol. xlii. p. 304, et seq.Google Scholar

page 437 note 4 I regret to have to make another serious complaint against Prof. Hull of having misquoted a passage from my published paper in the Phil. Trans., leaving out words essential to its meaning, and then stating that he has quoted the entire passage to avoid the possibility of misinterpretation, and that it is altogether unintelligible The passage in question, at the bottom of page 432 in my paper, is as follows, “Thus Dr. Bowerbank held that the sponges imbedded in the Chert of the Greensand possessed horny and not siliceous skeletons, and that the silica of the Chert in which they were imbedded was attracted from the exterior medium by the animal matter and not secreted therefrom by the living sponge.” In Prof. Hull's quotation the last paragraph runs thus, “The silica in the Chert in which they were imbedded was attracted from the exterior medium by the animal matter, and not secreted from the living sponge.” In the original I distinctly state that the living sponge secreted the silica now forming the Chert from the exterior medium (i.e. the sea-water). In the quotation, Prof. Hull omits the important words ‘these’ and ‘by,’ and then accuses me of not stating that the silica was originally derived from the sea-water!

Again, Prof. Hull on page 305 of his paper gives as a quotation from my paper, between inverted commas, the following passage, “The beds and irregular masses of Chert have been derived solely from the silica of the sponge-remains, instead of from that held in solution by the sea-waters themselves.” This passage, quoted as a verbatim extract, does not occur in my paper, and is not even a fair representation of my meaning, which will be seen by turning to pages 432, 3, to be, that the silica of the Chert was not derived directly from that held in solution in the sea-water.

page 439 note 1 loc. cit. p. 73.Google Scholar

page 440 note 1 Proc. Royal Soc. vol. xlii. p. 306.Google Scholar

page 440 note 2 Explanation of Sheet 128 (1859), p. 11.Google Scholar

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page 446 note 1 Proc. Royal Soc. 1887, vol. 42, p. 306.Google Scholar