Rock-structures in the Isle of Man and in South Tyrol

Abstract

MR. LAMPLUGH'S recent paper referred to in his letter in NATURE of April 26 (p. 612) is devoted to an elucidation of the “relations of the Carboniferous limestone to the Carboniferous volcanic rocks” in the Isle of Man (Q.J.G.S. 1900, p. 11). From Mr. Lamplugh's description, these relations are very similar to the relations which I described as subsisting between the Mid-Triassic dolomitic limestone (“Mendola Dolomite”) and the tufaceous “Wengen” beds of Enneberg. The “Buchenstein Agglomerate” of Enneberg, which I mentioned in my letter (NATURE, March 22), had been described in geological literature as a “Middle Triassic agglomerate” of local occurrence above “Mendola Dolomite,” in the neighbourhood of eruptive outbursts of that age. My map and sections showed that the agglomerate had a limited occurrence in fault-zones and overthrust-planes where differential movement had taken place between the harder, more resisting “Mendola Dolomite” and the yielding, mixed “Wengen” series “comprising dust-tuffs and lavas, as well as fossiliferous shales and shaly limestones.” I therefore explained the so-called “Triassic” agglomerate as a subsequent structure, of the nature of a shearbreccia, produced by the earth-movements of the later Alpine upheaval (Q.J.G.S. 1899, pp. 567, 584 Figs. 1, 4, 9, 10).