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Published online by Cambridge University Press: 01 May 2009
The groups of ophiolithic, that is, crystalline ferro-magnesian rocks in the comprehensive sense, to be dealt with in this and the subsequent paper are those west and east of Genoa. Of these the principal western or Voltri group was already referred to in the preceding paper as being, on its western margin, contiguous to the crystalline massif of Savona, and as constituting with the latter the geological contact-zone of the Alps and the Apennines. The anomaly of its position and petrological character is enhanced by the abrupt, clean-cut division of its eastern margin from the adjacent, more recent, and smaller ophiolithic group of Sestri and Isoverde, which is coeval with the groups of Eastern Liguria.
1 The term ophiolithic, though in its original and narrow sense it refers only to serpentines, applies to eruptive basic rocks or pietre verdi comprehensively, irrespective of age, like, e.g., the ‘roches ofitiques’ of the Pyrenees.Google Scholar
2 Geol. Mag., September, 1916, p. 400 et seq.Google Scholar
1 Mazzuoli, L. & Issel, A., “Sovraposizione nella Riviera di Ponente d'una zona ofiolitica eocenica ad una zona ofiolitica paleozoica”: Boll. Soc. ital., 1883, p. 44 et seq. “Zona di coincidenza delle formazioni ofiolitiche eoceniche e triassiche nella Liguria occidentale”: Boll. R. Com. geol., 1884, p. 2 et seq.Google Scholar
2 Rovereto, G., “Questioni dei calceschisti studiata in Liguria”: Boll. Soc. geol. ital., 1909, p. 408Google Scholar et seq. “Schisti e serpentine antichi in Liguria”: Atti Soc. Ligure Sc. nat., vol. ii, 4, 1891.Google Scholar
3 Franchi, S., “Massiccio cristallino ligure”: Boll. R. Com. geol., 1893, p. 43Google Scholar et seq. “Relazione campagna, 1911”: ibid., 1912, p. 41. “Posizione della zona a Helminthoidea labyrinthica nell'Eocene superiore”: ibid., 1915, p. 297. Franchi claimed the Voltri group as belonging to the Mesozoic calcschist and pietre verdi horizon of the Maritime and Cottian Alps in “Zona Pietre Verdi, Ellero e Bormida”, ibid., 1906, p. 89 et seq.
4 Both the Ligurian and the Apuan dolomitic limestone, independently analysed, contains 58 per cent carbonate of lime and 38 per cent carbonate of magnesia.Google Scholar
5 This superposition Mazzuoli and Issel regarded at the time as normal. They therefore assigned the calc-schists and pietre verdi to the Lower Trias, and figured these as such in their map of Liguria of 1887. The formation is now, like that of the Piémontese Alps, recognized as Upper Triassic.Google Scholar
1 De Stefani, C., “La zona serpentinosa della Liguria occidentale”: Rendiconti Atti R. Acc. Lincei, Roma, 1913, pp. 547 and 661 et seq.Google Scholar
2 Termier, P. & Boussac, J., “Passage latéral N.O. de Gênes de la série cristallophyllienne (schistes lustrés) à la série sédimentaire-ophiolitique de l'Appennin”: Comptes Rendus Acc. Sciences, Paris, 1911, p. 1361 et seq.Google Scholar
3 Sacco, F., “L'Age des formations ophiolitiques récentes”: Bull. Soc. belge de Géol., vol. v, 1891Google Scholar. Carta geologica Appennino centrale 1 : 100,000, Torino, 1891.Google Scholar
1 This section is deduced from Rovereto's more extensive one, op. cit., p. 414.Google Scholar
2 Professor Bonney described some of the coastal rocks between Sestri and Prà in “Notes on some Ligurian and Tuscan Serpentines”: Geol. Mag., May, 1879, p. 362 et seq.Google Scholar
1 Near Borzoli occurs the amygdaloidal calcareous diabase called borzolite, and west of Murta the cavernous variety called coschinolite by Issel. Madonna della Guardia is almost entirely built on diabase.Google Scholar
2 The serpentine of Pietra Lavarezza with associated ophicalce is overlain by diabase which forms the left bank of the upper Riasse torrent. In the Recreusi glen, where the unconformable contact of the Triassic limestone and the overlying Eocene argillaceous schist is conspicuously exposed, occur, along the junction of the Eocene ophiolithic rocks, large masses of Triassic gypsum which are quarried near Isoverde.Google Scholar