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II.—The Ophiolithic Groups of the Ligurian Apennines. II. Eastern Liguria
Published online by Cambridge University Press: 01 May 2009
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The three principal ophiolithic groups of this region are those of Levanto, Monte Bianco, and Monte Penna, about midway between Spezia and Genoa, viz. north of Levanto, Sestri Levante, and Chiavari, at average altitudes of 300, 800, and 1,600 metres respectively. Like the Eocene ophiolithic group of Sestri Ponente and Isoverde, west of Genoa, they lie in the upper horizon of that formation, that is, in the fossiliferous (fucoids) albarese limestones and the argillaceous schists which rest on the Middle Eocene macigno sandstone as the lowest member of the Ligurian Eocene. The sedimentary and infolded ophiolithic groups consecutively aligned from the coast to the crest of the Apennines form a series of anticlines north to south, dipping west, with some transverse folds. The whole region is greatly contorted and brecciated; it is, moreover, profoundly eroded by torrents charged with calcium carbonate which has accelerated erosion and at the same time re-cemented breccia. Although the three groups are now separated, they are, together with the scattered islands north of the crest of the Apennines towards Piacenza in the Po Valley, only the remnants of an originally continuous formation of no less than 1,500 square kilometres or 600 square miles.
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page 489 note 1 Indurated, silico-argillaceous schists are known as galestri, yellowish, red, or green in colour; ardesia are tegular, silico-argillaceous-calcareous schists ; and resinite is a white or yellowish siliceous, semi-opaline variety.
page 490 note 1 Some of the rocks near Levanto were described by ProfessorBonney, in op. cit., Geol. Mag, 1879, p. 362 et seq.Google Scholar.
page 490 note 2 Specimens of the Pignone group were examined microscopically by ProfessorCossa, A. of Turin, who also gives analyses of the same in comparison with some of the similar Ligurian and Tuscan rocks (Boll. R. Com. geol., 1881, p. 246 et seq.).Google Scholar.
page 493 note 1 These sections are deduced from Lss. Mazzuoli's in “Formazioni ofiolitiche della Riviera di Levante, Liguria”: Boll. R. Com. geol., 1892, p. 2 et seq.Google Scholar.
page 494 note 1 See an earlier memoir by Mazzuoli, L. &Issel, A., “Studi sulle masse ofiolitiche della Riviera di Levante”: Boll. R. Com. geol, 1881, p. 313 et seq.Google Scholar.
page 495 note 1 Mazzuoli, L., “Formazione ofiolitica nella Valle del Penna”: Boll. R. Com. geol., 1884, p. 384 et seq.Google ScholarCossa, A., “Intorno ad alcune roccie della Valle del Penna nell'Apennino ligure”: Rendiconti R. Accad. Lincei, Roma, 1886, pp. 502 and 643 et seq. Professor Cossa, of Turin, also first examined microscopically some of the ophiolithic rocks on the north of the ApenninesGoogle Scholar : “Sopra alcune roccie serpentinose dell'Apennino Bobbiese,” Boll. R. Com. geol., 1881, p. 58 et seq.Google Scholar; also Zaccagna, D., Relazione, 1902Google Scholar; Ibid.., 1903, p. 39.
page 496 note 1 Further east towards Spezia the Mesozoic and Tertiary sedimentary strata exhibit an abnormal superposition which has always been regarded as an extensive inverted fold, but may be the effect of an overthrust. In the ophiolithic areas of Eastern Liguria, on the other hand, the Eocene sedimentary sequence is normal.