On the Crystalline Schists of the Alps. 285 



lite (Tremola-) schists of the St. Gothard and then gneiss ; on the south 

 side gneiss. There is also some rauehwacke. This rock, at first 

 sight, appears to underlie the Piora-schists, and thus to he the lowest 

 member of a trough. If so, as it is admittedly about Triassic in 

 age, the Piora-schists would be Mesozoic. The author shows that (1) 

 the latter rocks do not form a simple fold ; (2) they are beyond all 

 question altered sediments ; (3) they have often been greatly crushed 

 subsequent to mineralization ; (4) the garnets, staurolites, &c. (if 

 not injured by subsequent crushing) are well developed and charac- 

 teristic, and are authigenous minerals. 



(3) The Rauehwacke and its Relation to the Schist. 



(a) The Val-Piora Sections. — The author shows that the raueh- 

 wacke, which at first sight seems to underlie the dark mica-schist, 

 is inconstant in position (on the assumption of a stratigraphical 

 sequence) ; that its crystalline condition does not resemble that of 

 the schist- series, but is rather such as is common in a rock of its 

 age ; that it contains mica and other minerals of derivative origin, 

 and in places rock-fragments which precisely resemble members of 

 the Piora-schist series. 



(b) The Val-Canaria Section. — This section, described by Dr. 

 Grubenmann, is discussed at length. It is shown that the idea of a 

 simple trough is not tenable, for identical schists occur above and 

 below the rauehwacke ; that there is evidence of great pressure, 

 which, however, acted subsequently to the mineralization of the 

 schists ; and that in one place the rauehwacke is full of fragments 

 of the very schists which are supposed to overlie it. 



(c) Nv.fenen Pass §e. — Other cases, further to the west, are 

 described, where confirmatory evidence is obtained as to great 

 difference in age between the rauehwacke and the schists, and the 

 antiquity of the latter. The apparent interstratification is explained 

 by thrust-faulting, 



(4) The Jurassic RocJcs, containing Fossils and Minerals. 



The author describes the sections on the Alp Vitgira, Scopi, and 

 the Nufenen Pass. Here indubitable Belemnites and fragments of 

 Crinoids occur in a dark, schistose, somewhat micaceous rock, which 

 is often very full of "knots" and "prisms" of rather ill-defined 

 external form, something like rounded garnets and ill-developed 

 staurolites. These rocks at the Alp Vitgira appear to overlie, and 

 in the field can be distinguished from the black-garnet schists. In 

 one place the rock resembles a compressed breccia, and among the 

 constituent fragments is a rock very like a crushed variety of the 

 black-garnet mica-schist. These Jurassic "schists" are totally 

 different from the last-named schists, to which they often present 

 considerable superficial resemblance ; for instance, their matrix is 

 highly calcareous, the other rock mainly consisting of silicates. 



