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IV.—Schists and Schistose Rocks in the Lepontine Alps: Reply to Criticisms by Professor A. Heim
Published online by Cambridge University Press: 01 May 2009
Extract
Some three years ago, on referring to the twenty-fifth volume of the “Beiträge zur Geologischen Karte der Schweiz,” I found Professor Heim had devoted a few pages (pp. 316–319) of that work to my criticisms of his attempts to prove that Jurassic rocks had been metamorphosed into schists containing authigenous garnets, staurolites, etc. Had he brought forward any new fact of importance or pointed out any serious error in my work I should have replied at once, but as he was unable to do this, and as the justice of one of my criticisms was indirectly admitted in the petrographical appendix by Dr. C. Schmidt, I allowed more pressing and interesting matters to take precedence of one which had become chiefly personal.
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References
page 162 note 1 Compte Rendu de la 4me Session, p. 80. See also Nature, 09 27 and 10 4, 1888Google Scholar, and Quart. Journ. Geol. Soc., vol. xlvi (1890), p. 236Google Scholar.
page 162 note 2 Geol. Mag., 1900, p. 215Google Scholar.
page 162 note 3 Quart. Journ. Geol. Soc., vol. xlvi (1890), p. 67Google Scholar; vol. 1 (1894), p. 285Google Scholar; vol. liii (1897), p. 16Google Scholar.
page 163 note 1 Quart. Journ. Geol. Soc., vol. xlvi (1890), p. 219Google Scholar, and vol. xlix (1893), p. 89Google Scholar.
page 163 note 2 I suppose from what I have read that Professor Heim will refuse to call these rocks crystalline schists. If so, there is no crystalline schist—either garnet-mica, calc-mica, staurolite-mica, or quartz-mica schist—in any part of the Alps that I know of.
page 163 note 3 The situation of the outcrops and their breadths make it impossible to escape this difficulty by supposing one black garnet schist to have been the top bed and to be doubled back on itself.
page 164 note 1 Dr. Schmidt admits the presence of clintonite (which name is now applied by Dana to the group including the species of chloritoid), and assigns the knoten and prismen to zoisite. Both minerals are so full of impurities that it is very difficult to come to any conclusion, but neither reminds me of zoisites, nor is any close relationship suggested by the analyses (quoted on p. 233 of my paper); and after reconsideration of my specimens I see no reason to change what I wrote in 1890 (Quart. Journ. Geol. Soc., vol. xlvi, pp. 232–234Google Scholar). Dr. Schmidt's petrographical description will be found in Beiträge, vol. xxv, Anhang, pp. 41–65Google Scholar.
page 164 note 2 Beiträge, ut supra, p. 317.
page 164 note 3 Though I think that, as a rule, I can distinguish a marble belonging to a group of crystalline schists from an ordinary Palæozoic or later limestone, even if pressure modified, I put more reliance on any silicates which may be associated with the calcite, and do not feel quite happy unless I can trace the rock into some schist composed largely of these.
page 165 note 1 I may add that the general tendenz to minimize the effect of ‘dynamo-meta-morphism,’ of which he accuses me (p. 316), has the same foundation. That is an important factor in producing change, but its effect has been often greatly overestimated. After ten years' work I adhere to the position adopted in 1890 (loc. cit., p. 223). which since then I have so often expressed that I am weary of repeating it.
page 166 note 1 Quart. Journ. Geol. Soc., vol. xliv (1888), p. 11Google Scholar.
page 166 note 2 See MissRaisin, C. A.: Quart. Journ. Geol. Soc., vol. lvii (1901), p. 55CrossRefGoogle Scholar. A museum specimen labelled Pyreneite (from that mountain range) appears to be another instance.
page 166 note 3 See Quart. Journ. Geol. Soc., vol. xlv (1889), pp. 96–99Google Scholar.
page 166 note 4 This is a transcript of my field notes, in which I do not pick my phrases. I probably should not now use the words ‘knoten schiefer.’ What I meant to express was that it seemed in about the same state of alteration as a chiastolite slate.
page 166 note 5 A fortnight later I paid my first visit to the Val Piera.