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IV.—The Crystalline Rock-areas of the Piémontese Alps
Published online by Cambridge University Press: 01 May 2009
Extract
In the preceding paper I described the crystalline rock-areas of the Maritime and Cottian Alps: I now proceed to briefly review those of Northern Piémont forming part of the Grajan and Pennine Alps, under three heads—
I. The Lanzo Valleys and Gran Paradiso Groups.
II. The Dora Baltea (Val d'Aosta) Area.
III. The Lanzo, Ivrea, and Val Sesia Area.
They are shown in the sketch-map, Fig. 1. The conclusions in reference to the combined areas of the Piémontese Alps will be stated at the end of the present paper.
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References
page 304 note 1 Geol. Mag., 05 and 06, 1916, pp. 198–205, 250–5Google Scholar.
page 305 note 1 The three Stura valleys, as also the Orco Valley (Gran Paradiso), are easily accessible by roads leading to Usseglio, Balme, Forno, and Ceresole at the upper ends, 1,265, 1,458, 1,226, and 1,613 m. altitude respectively. The Usseglio and Balme Valleys are also known as the Viù and Ala Valleys respectively.
page 305 note 2 The short valley of the Tesso, immediately north of Lanzo, lies, strictly speaking, outside the drainage area of the St. Ignazio defile, but the torrent, rising in Cima Angiolino, belongs to the Stura watershed and forms part of the Lanzo valleys.
page 307 note 1 Boll. R. Com. geol., 1905, p. 191Google Scholar. At the time of the compilation of this map all the crystalline rocks of the Lanzo valleys were still considered of Archæan age without distinction between the age of the mica-schist and the calc-schist formation, the new classification dating from 1911.
page 307 note 2 The earlier works dealing with the Lanzo valleys, etc., by Gastaldi, Strüver, Baretti, and Bucca from 1871 to 1886 were already quoted in the preceding papers.
page 307 note 3 The local designations Uja, Ciama, Punta, Becca, Bric, Truc, Torre, Rocca, etc., all denote point, peak, summit, crest, crag, etc.
page 309 note 1 In a valuable memoir, “Contribuzione allo studio delle roccie a glaucofane, etc., Liguria e Alpi Occid.,” Boll. R. Com. geol., 1903, p. 255 et seq.Google Scholar, S. Franchi has shown that the crystalline sedimentary rocks of the Piémontese Alps, such as silico-calcareous schists (diaspri), quartzites, calc-schists and limestone, mica-schists, phyllites, and minute gneiss, contain glaucophane, epidote, sismondina, zoisite, chlorite, albite, and other secondary minerals as the result of metamorphism of associated and intercalated eruptive material.
page 309 note 2 Novarese found a granite vein in a large erratic gneiss block near the Sea Glacier (2,500 m.) in the south-west corner of the Paradiso massif, which may therefore contain intrusive granite, like the Argentera massif in the Maritime Novarese, Alps. V., “Rilevamento Valli Orco e Soana, Alpi Occid.”: Boll. R. Com. geol., 1894, p. 215 et seqGoogle Scholar. A. Stella, “Rilevamento Valle Orco, Alpi Occid.”: ibid., p. 343 et seq.
page 310 note 1 The whole region between the Aosta and Orco Valleys, including the Paradiso massif, is, perhaps more than any other part of the Piémontese Alps, rendered conveniently accessible by the numerous mule paths of the Royal shooting preserves. An excellent topographical map of the Val d'Aosta, Lanzo, and Ivrea region, 1 : 250,000, is that by Novarese, V. in Boll. R. Com. geol., 1913–1914, p. 244, “Il Quarternario Valle d'Aosta e Valli Canavesi.”Google Scholar
page 310 note 2 Villeneuve is one of the localities where S. Franchi found fossils in Triassic limestone intercalated in calc-schists. “Terreni secondarie facies Piémontese”: Boll. R. Com. geol., 1909, p. 526 et seqGoogle Scholar.
page 311 note 1 This section is founded on the complete one given by Novarese in “Profilo della Grivola”, ibid., p. 497 et seq.
page 311 note 2 Baretti, M., “Studi Gruppo Gran Paradiso”: Mem. Acc. Linceo Torino, 1876, p. 195 et seqGoogle Scholar.
page 311 note 3 Novarese, V., “Diorite granitoide e gneissiche Val Savaranche”: Boll. R. Com. geol., 1894, p. 275 et seqGoogle Scholar.
page 311 note 4 The calc-schists of Grivola and Galisia were assigned to the Mesozoic (Lias-Trias) as the equivalents and continuation of the schistes lustrés by Bertrand, M. in his “Etudes dans les Alpes françaises”, Bull. Soc. géol. France, vol. xxii, p. 69 et seq., 1894Google Scholar, which marked his return from his temporarily Archæan to his earlier Mesozoic views on that formation. The latter were confirmed by Termier, P. in “Les schistes lustrés de la Grivola”, Bull. Service Carte géol. France, vol. vii, p. 150 et seq., 1895Google Scholar. The Piémontese calc-schists are, on the whole, more micaceous than the French schistes lustrés, which are more aluminous than the former and to which the designation “série cristallo-phyllienne” is therefore more appropriate. The superposition of calc-schists on Triassic limestone as verified by Franchi and Termier in various localities also occurs in the Roches d'Ambin massif (Petit M. Cenis, upper Susa Valley), where the minute gneiss and mica-schist are overlain by limestone upon which rests calc-schist.
page 312 note 1 Stella, A., “Gneiss Monte Emilius e M. Rafré”: Boll. Soc. geol. ital., 1906, p. xlviGoogle Scholar. Mattirolo, E., “Rilevamento Val Champorcher, Alpi Graje”: Boll. R. Com. geol., 1899, p. 3 et seqGoogle Scholar.
page 313 note 1 Novarese, V., “Gneiss Monte Emilius e M. Mary”: Boll. Soc. geol. ital., 1912, p. 31Google Scholar. Novarese describes an interesting section of granite, mica-schist, and diorite in a railway cutting between Aosta and Quart, on the left of Dora, below M. Mary.
page 313 note 2 Lugeon, M. & Argand, E., “Grandes Nappes de Recouvrement de la zone du Piémont. Homologies ditto”: Comptes rendus Acad. Sciences, Paris, Mai 15 et 29, 1905Google Scholar.
page 313 note 3 “Relazione”: Boll. R. Com. geol., 1906, p. 27Google Scholar.
page 313 note 4 Novarese, V., “Profilo Grivola”: Boll. R. Com. geol., 1909, p. 497 et seqGoogle Scholar. Stella, A., op. cit., 1912, p. xlviGoogle Scholar. “Problema geo-tettonico Ossola e Sempione”: Boll. R. Com. geol., 1905, p. 5 et seqGoogle Scholar. S. Franchi, “Tettonica della Zona del Piemonte”: ibid., 1906, p. 123 et seq.