Page:The Journal of geology (IA journalofgeology11893univers).pdf/436

ination to be altered volcanic material in conformable layers. Farther west, where these same rocks become tightly compressed between the gneisses of the central massifs, they have become recrystallized in proportion to the amount of their dislocation. "The study of the Bündnerschiefer," says Heim, "was that which years ago first convinced me of the possibility and reality of crystalline metamorphism being produced without the agency of eruptive contact, since I here for the first time observed how a belemnitiferous calcareous argillite became gradually more and more crystalline by the development of such minerals as mica, garnet, hornblende, zoisite, etc., at first as indistinct and imperfect nodules, and later as good crystals" (l. c., p. 52). The Bündnerschiefer, both in their less altered localities and in occasional beds, which have been by chance saved from metamorphism, are quite rich in Jurassic fossils.

About one-half of Professor C. Schmidt's appendix to Professor Heim's monograph is devoted to the petrographical description of the Bündnerschiefer, while the remainder treats of the crystalline rocks of the Aar, Gotthard and Adula massifs. A few preliminary remarks on the melaphyre of the Kärpfstock supplement the author's earlier communications with reference to the eruptives occurring in the Glarner double-fold.^[1] The rocks from the three crystalline massifs are mainly the characteristic Alpine gneiss-granites or protogine, with dioritic or amphibolitic interpositious. Sericite- ottrelite- paragonite- zoisite- glaucophane-schists and eclogites also occur. The Adula gneiss is characterized by a green potash-mica (phengite) which is both uniaxial and biaxial. The rocks of the Bündnerschiefer are described by Schmidt under two principal heads: a) gray and black schists which are more or less completely metamorphosed sediments; and b), green schists which are foliated and metamorphosed eruptive material. Under the first division are mentioned schists with newly crystallized chloritoid, zoisite, tourmaline, epidote, biotite, muscovite, quartz, plagioclase and rutile. In some cases complete pseudomorphs of zoisite after echinoid remains are to be found. Other more tightly compressed beds at Nufenen, Val Piora, Lukmanier, Scopi, Ariolo, and other localities are still more highly crystalline, containing disthene, garnet, staurolite and similar minerals in abundance. These rocks have also been petrographically studied by Prof. U. Grubenmann.^[2]