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1889; Nature Portfolio; Volume: 40; Issue: 1027 Linguagem: Inglês
10.1038/040220a0
ISSN1476-4687
ResumoTHIS pamphlet gives a summary of the views entertained at the present time by many leading Swiss geologists as to the geological history of the Alps. So far as we can see, it does not profess to be more than a compilation, or to contain any original work; but as a summary it is as clear and concise as the subject permits. The author, in the first chapter, briefly sketches the history of the principal types of rock which enter into the composition of the Alps; and, as might be expected at the present juncture, lays much stress upon the results of pressure. Some, indeed, may think that the present moment is rather inopportune for such a memoir as this; for the modifications due to pressure, especially in rocks already crystalline, are still the subject of so much controversy among geologists, that it is difficult to know what may be taken for granted; and there is a danger, if the writer be a disciple of the new school, of confusing the results of demonstration and of hypothesis. A quotation (translated) will indicate the author's point of view better than a general statement. After pointing out that two great rock groups exist in the Alps, one consisting of various granitoid rocks, gneisses, and crystalline schists, the other of limestones, sandstones, and other sediments, he proceeds —“ In Switzerland the region which intervenes between the two zones is not very broad. The general strike of this intermediate zone is through Coire, Ilanz, the Greina Pass, Scopi, Airolo, Nufenen, the Rhone Valley, to Martigny, and so through the Val Ferret to the Little St. Bernard. The rocks of this intermediate zone are crystalline sediments, the age of which it is difficult to fix with precision. In the Grisons they have lately been claimed by Gümbel as Palæozoic, in the Valais they have been shown by Lory to be Triassic: that the same, from the Greina Pass to the Nufenen, are Jurassic, can be proved by fossils.” This, however, begs the whole question. It has yet to be shown that the Swiss geologists have not confused together, as some maintain, two distinct rock groups, owing to their having mistaken (not for the first time) for crystalline schists, deposits which only simulate the latter, because they are locally composed almost entirely of their débris.
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