On the Crystalline Schists and their Relation to the Mesozoic Rocks in the Lepontine Alps

Abstract

At the close of the year 1888 I read before this Society a paper “ On two Traverses of the Crystalline Rocks of the Alps,“ in which I maintained that these rocks could be arranged in certain fairly definite groups, which exhibited a stratigraphical succession. On this communication only two criticisms of importance were offered. Of these one expressed a doubt of the value of the method which I had adopted in my work; the other affirmed that certain schists, regarded by me as members of a very ancient series, probably Archæan, had been demonstrated by the presence of Mesozoic fossils to be of the latter age ; or, in other words, that, in the Alps, ordinary sediments deposited in the Jurassic epoch had been subsequently converted into true crystalline schists, a result of metamorphic action which I had implicitly affirmed to be incredible. The former criticism, which amounted to an assertion that the general succession of the Alpine rocks could only be ascertained by very detailed mapping, in my opinion, indicated an imperfect knowledge of the subject, while it was scientifically unsound and historically incorrect. It indicated an imperfect knowledge, because, as a matter of fact, a considerable part of the Alps has already been mapped, not by irresponsible amateurs but by official surveyors, and it was with the interpretation of these maps that I was largely concerned; and because it assumed that an impossibility could be performed.As I have had the honour to fill the same position in the Alpine Club that I have done in this Society, I may be affirm without fear of contradiction that a very elaborate petrographical mapping of the Alps is impossible ; for the most painstaking and conscientious of surveyors must assume much that is incapable of demonstration.