Petrological Abstracts and Reviews 



Edited by ALBERT JOHANNSEN 



Koenigsberger, Joh. Erlduterungen zur geologischen und mine- 



ralogischen Karte des dstlichen Aaremassivs von Disentis bis 



zum Spannort. Freiburg i. B. und Leipzig: Speyer & Kaer- 



ner, 1910. Pp. 63; figs. 8; colored geological map in pocket. 



This work is a geological description of a small portion of the Alps, 



12X26^ km. in extent, between Disentis and Spannort, and just north 



of St. Gotthard. It' is mapped on a scale of 1 cm. to 500 m., on one of 



the beautiful maps of the Swiss Topographic Bureau in Berne. 



The author tentatively submits the following sequence: 



1. Deposition of pre-Carboniferous sediments. These were much 

 altered by the later intrusives and are now chiefly sericite gneiss. 



2. Intrusions of diorite, diorite porphyrite, diabase, and gabbro- 

 peridotite into Silurian and Devonian rocks. The intrusives are almost 

 entirely altered to amphibolites but the original rocks in most cases 

 can be determined. The diorites are accompanied by differentiation 

 zones of diorite-aplite. 



3. Intrusions of gneiss, probably originally granite, into upper- 

 Devonian rocks, and forming a low-arched laccolith. By this intrusion 

 the former eruptives and the sediments were metamorphosed into 

 crystalline schists. 



4. Intrusions of syenite, followed by biotite and hornblende granite 

 (Piz Ner), of middle or upper Carboniferous age. 



5. Intrusion of the Aar granite at the contact and beneath the 

 previously intruded syenite. In places fragments of the latter are 

 inclosed in the former. Contemporaneously with the intrusion came 

 the Carboniferous folding, seen in the Wendeljoch. 



6. The Jura-Trias folding and thrust faulting of the Alps followed 

 next and produced further metamorphism. Nowhere are there exposed 

 in the Aar massif any contemporaneous intrusives. 



The rocks are briefly described, numerous analyses are given, and 

 the contact effects are shown. The mineral localities are described, 

 seven excursions are outlined, and complete literature references are 

 given. 



Albert Johannsen 



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