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VI.—Devonian Greenstones and Chlorite Schists of South Devon

Published online by Cambridge University Press:  01 May 2009

C. A. Raisin
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Extract

In a paper published in the Devonshire Transactions for 1888 (p. 215), Mr. Somervail suggests the identity of the chlorite schists of South Devon with certain rocks to the northward. As this hypothesis (could it be established) would have a most important bearing on subjects of controversy, I took the opportunity in a few days this winter, to visit and collect from these localities, including the dyke nearest to Toreross. I was not rewarded by finding any striking similarity to the metamorphic rocks of the south. In that series, the chlorite schists consist of clear and definite crystalline grains, among which I find felspar to be rare and have not yet certainly identified augite—while these northern greenstones are full of broken crystals of both minerals, together with viridite, dust resulting from the crushing, and a small amount of minute secondary hornblende and sericite (?), chlorite being generally rare, and often absent.

Type
Original Articles
Information
Geological Magazine , Volume 6 , Issue 6 , June 1889 , pp. 265 - 269
Copyright
Copyright © Cambridge University Press 1889

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References

page 266 note 1 Q.J.G.S. 1884, vol. xl. p. 8, fig. 4, p. 22.Google Scholar

page 266 note 2 Q.J.G.S. 1876, vol. xxxii. p. 407Google Scholar, Allport, S.. Q.J.G.S. 1876, vol. xxxii. p. 155, and 1878, vol. xxxiv. p. 471,Google Scholar Phillips, J. A.. Q.J.G.S. 1880, vol. xxxvi. p. 285, and 1886, vol. xlii. p.392,Google Scholar Rutley, F.. Brit. Petrogr. J. J. H. Teall, p. 228Google Scholar.

page 266 note 3 Somewhat like the Carlion rock (No. 7) of MrRutley, , Q.J.G.S. 1886, p. 397.Google Scholar The augite resembles that of fig. 2, p. 398.

page 266 note 4 Cf.MrAllport, , Q.J.G.S. 1876, p. 419.Google Scholar

page 266 note 5 As, for example, in the Lizard gabbro and basalt. Q.J.G.S. 1877, vol. xxxiii. pp. 904, 907,Google Scholar Prof. Bonney, “On the Serpentine and Associated Rocks of the Lizard.” See also Q.J.G.S. 1885, vol. xli. p. 520,Google Scholar “On the so-called Diorite of Little Knott,” and Q.J.G.S. 1883, vol. xxxix. p. 256,Google Scholar “On Hornblende Picrite from Anglesey,” Prof. Bonney. Also Q.J.G.S. 1878, p. 493,Google Scholar J. A. Phillips. “Perimorphic ” hornblende of MrHarker, , Q.J.G.S. 1888, vol. xliv. p. 452.Google Scholar

page 266 note 6 Amer. Journ. Science, 1887, vol. xxxiii. p. 388, fig. 3;Google Scholar also U. S. Geol. Survey, 5th Rep. 1883–4.

page 266 note 7 Cf. Brit. Petrogr. Teall, J. J. H., pp. 216, 230.Google Scholar

page 267 note 1 Q.J.G.S. 1886, vol. xlii. p. 393, pl. xii. figs. 1, 3.Google Scholar

page 267 note 2 Q.J.G.S. 1878, vol. xxxiv. p. 483, pl. xx. fig. 2.Google Scholar

page 268 note 1 Trans. Devon Assoc. 1888, p. 224.Google Scholar

page 268 note 2 Thus these rocks in the direction of their micaceous constituent would agree with the phyllites described by Professor Bonney from near Morlaix, Q.J.G.S. 1888, vol. xliv. p. 13,Google Scholar and would differ from those near Torcross, Q.J.G.S. 1884, vol. xl. p. 17.Google Scholar

page 268 note 3 See map Q.J.G.S. 1887, vol. xliii. p. 715.Google Scholar The dotted line marking the junction of phyllites and metamorphic rocks should probably cross the stream about east of the l of Muckwell, before bending south-eastward or E.S.E. to the coast. This alteration does not, however, disprove the possibility that the fault may have determined the lower course of the valley, since there are no exposures which we can trust along the 400 yards between the quarry and the beach; and also in a continued erosion along a fault, a portion of one rock may often be left adhering at some spot to the mass against which it was faulted.

page 269 note 1 Trans. Dev. Assoc. 1888, vol. xx. p. 217.Google Scholar