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I.—The Geological Age of the Carrara Marbles
Published online by Cambridge University Press: 01 May 2009
Extract
The statuary marbles of Carrara have been repeatedly asserted to be metamorphic limestones of earlier Mesozoic or later Palæozoic age. Similar statements were once frequent in regard to other mountain regions, but they have one by one dropped out of geological literature. This, however, is such a hardy perennial as to be still repeated in petrological and other textbooks. Doubts, however, were felt by the first author in 1878, and these became almost certainties after 1886, but as each visit was only for a few hours, and did not allow of a proper examination of the rocks in situ, he deferred writing on the subject till he could spend a longer time at Carrara. That opportunity, however, never came, and is not now likely to occur ; but on finding not long since that his friends, Professor Boyd Dawkins and the Rev. H. H. Winwood, had visited the quarries in 1898, and the latter had published an account of the district, with a sketch-section drawn by the former, he communicated with them, and the following paper summarizes the experience of the three, which it is hoped may help in laying another metamorphic ghost.
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References
page 289 note 1 See, for example, Text-book of Petrology, vol. ii, Sedimentary, Hatch, F. H. and Rastall, R. H., 1913, p. 250.Google Scholar In books of earlier date the marbles are said to be Lower Jurassic, Building and Ornamental Stones, Hull, E., 1872, p. 127Google Scholar; Triassic, Traité de Géologie, de Lapparent, A., 1906, p. 1100Google Scholar; Upper Triassic on the Carta Geologica della Liguria, by Issel, A. and Squinabol, S. (1891)Google Scholar, and they are associated with micaceous schists in a short text published with the map. They are assigned to the same age in a description of an excursion to Carrara, Bollettino della società Geologica Italiana, vol. xxi, p. 163, 1902,Google Scholar which classes some underlying schists and marbles as Permo-Carboniferous, and some schists beneath those as indeterminate Palæozoio, and gives the following succession of the overlying beds, from the base of the Miocene sandstones and conglomerates: Eocene, sandy and calcareous strata; Upper Cretaceous, varied deposits; Lower Cretaceous, limestones; Tithonian, Lias and Rhætic, various; all these being more or less fossiliferous. Jervis, W. P., however, I Tresori sotteranei dell'Italia, vol. iv, p. 261, 1889,Google Scholar regards the marbles as pre-Palæozoic. A summary of Italian opinion prior to 1878 is given in this Magazine by Professor G. A. Lebour (1878, pp. 289 and 382). He adopts Coquand's verdict for a Carboniferous age.
page 289 note 2 Unfavourable weather made both shorter than had been intended.
page 289 note 3 Proceedings of the Cotteswold Naturalists' Field Club, vol. xiii, p. 57.
page 289 note 4 For the paragraph marked thus § Mr. Winwood is mainly responsible; for those marked thus ¶ Professor Bonney.
page 290 note 1 So called, I have been informed, because at one time it was conveyed to Sicily and exported thence to other places.—T. G. B.
page 290 note 2 There are other quarries of different varieties of marble, one important group being near Seravezza, to the south-east of Carrara and Massa. See Vasari on Technique, edited by Brown, G. B., 1907, pp. 45–8 and 119–26.Google Scholar
page 291 note 1 I think he gave it to me shortly before my visit in the autumn of 1886, remarking at the time: “Here is a gneiss of Triassic age from near Carrara.” My reply was to this effect: “If you had told me you got the specimen not far from the St. Gotthard, on the northern side of the Val Bedretto, I should not have been surprised. Was there in the field an actual sequence from it to indubitable Triassic rock?” “Not exactly,” he answered, “but they were exposed on opposite sides of a valley.” “Well, then,” said I, “a fault may have gone down that valley, so, though greatly obliged to you for the specimen, I cannot admit that it has been proved to belong to the Triassic system.”—T. G. B.
page 291 note 2 See Presidential Address to the Geological Society, Quart, Journ., vol. xlii, Proc., p. 65, 1886. See also id., vol. xlvi, pp. 202–4, 1890Google Scholar, and other papers of mine on Alpine schists.—T. G. B.
page 292 note 1 Mr. R. H. Rastall, who has had considerable experience in examining microlithic minerals, informs me that the colouring matter appears to him mainly external and suggests brookite as a possible identification.
page 292 note 2 It shows the gneissose aspect to be illusory, the apparent felspar granules being due to pulverization of the quartz.
page 293 note 1 Quart. Journ. Geol. Soc., vol. xlv, p. 95, 1889.Google Scholar
page 293 note 2 Perhaps also to the quartz-rock of the Twelve Pins, which I have not actually visited.
page 293 note 3 For which and other interesting specimens of marbles I have to thank Mr. W. Brindley, of Westminster.
page 293 note 4 In the Binn Valley crystalline dolomites are interbedded with dark mica schists.
page 293 note 5 This is asserted to be Cretaceous (Hatch and Rastall, ut supra, p. 250). I have seen a little of this neighbourhood and am unable to accept the identification.
page 295 note 1 After careful examination I formed the opinion that the apparent interbedding was illusory, and that they were nipped in by thrust faults. Where, however, the marble was associated with the calc-mica schists it obviously graduated into these.