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Published online by Cambridge University Press: 01 May 2009
In the Devonian sandstones and grits of Torbay abundant quartz veins are occasionally developed, indicating a moderate amount of heat. Neither the quartz-grains nor occasional fragments of felspar are to any extent affected.
At Dartmouth, on the raised-beach platform, quartz is largely developed together with a little felspar and chlorite, indicating sufficient heat to form or re-form these minerals. At Slapton Sands the grits are about the same as in Torbay: felspar granules remain angular and intact.
Between Beesands village and Tinsey Head the quartz-grains occasionally show signs of incipient solution, as also do the tourmalines. In one slide (No. 5) the approach of schistosity seems to be heralded by minute roughly parallel cracks cemented by iron ores and a pale-green mica. Minute crystals of pyrites, some rectangular, are formed in the rock. At the Start, in rare cases, grains or remnants of grains of original granitic quartz can be detected in the schist. Tourmaline is partially dissolved with recrystallization.
page 341 note 1 Plate 7, fig. 2.
page 341 note 2 Plate 7, fig. 1.
page 341 note 3 Plate 6, fig. 2.
page 342 note 1 Appendix, slide 40.
page 342 note 2 Geologie Experimentale, vol. i. p. 207.Google Scholar
page 342 note 3 Elements of Chemistry, vol. ii. (third edition), p. 509.Google Scholar
page 342 note 4 In these rocks there is often a marked alineation of the felspar.
page 343 note 1 Phil. Mag. ser. 4, vol. xlvi. pp. 30, 31.Google Scholar
page 345 note 1 In siliceous band south of Hope Headland.
page 346 note 1 e.g. Eastern Caernarvonshire: cf. Harker; Bala Volcanic Series of Caernarvonshire, pp. 83, 117; 1889.
page 347 note 1 Plate 8, fig. 1.