376 



The Vosges supplies us with a case in which the altered rock is very 

 uniform in composition over considerable areas, and in which only one 

 kind of intrusive rock (granitite) occurs on a sufficiently large scale to 

 produce important effects. The south of Norway, on the other hand, 

 supplies us with a case in which several varieties of eruptive rock have 

 affected a variable group of sedimentary deposits. The metamorphic 

 phenomena of this region have been the subject of investigation by 

 Messrs. KJERULF^ and BROGGER.^) The following account is taken 

 from an elaborate memoir by the latter observer. The eruptive rocks 

 comprise sphene-bearing hornblende-granite, hornblende-syenite, granitite, 

 mica-syenite, augite-syenite and nepheline-syenite. The sedimentary rocks, 

 on which the principal observations have been made, belong to the Olenus 

 and Asaphus stages of the lower Palaeozoic. They comprise argillaceous 

 and calcareous deposits of various degrees of purity. The following general 

 laws have been established by the work of KJERULF and BROGGER. 



(1) There is, as a rule, no alteration in the composition of the eruptive 



rock in the immediate neighbourhood of the junction. The 

 change observed is merely one of texture. 



(2) The different kinds of eruptive rock produce the same effects 



in the same kind of stratified rock. 



(3) The junction between the intrusive and sedimentary rocks is 



always perfectly sharp. There is no sign of melting. 



(4) The intensity of the metamorphism in any particular bed increases 



as the junction is approached. 



(5) At the same distance from the eruptive rock each bed is meta- 



morphosed in a manner depending on its composition. 



The lowest rocks of the series investigated by BROGGER are dark 

 bituminous and pyritous shales (alum-shales or slates), containing nodules 

 of bituminous limestone. The dark shales become harder and lighter 

 in colour as the junction is approached, and innumerable small spots 

 make their appearance. The spots are rarely more than ^ mm. in diameter. 

 As in the Steiger Schiefer they are due to a local accumulation of 

 pigment. In some localities the spots are not developed, the rocks in 

 question becoming either black hornfels or chiastolite-slate. Alternations 

 of black hornfels and chiastolite-slate may sometimes be observed. The 

 calcareous nodules (stinkkalkellipsoide) are changed to a violet hornfels 

 mainly composed of crystalline silicates (kalksilikathornfels). The prin- 

 cipal minerals of these nodules are vesuvianite, felspar (mostly labradorite 

 or anorthite), wollastonite, augite, hornblende and calcite. The plagioclase 

 occurs in irregular colourless grains, often showing a tendency to the 

 lath-shaped form, and having the characteristic twin structures well 

 developed. The extinction angles indicate that the dominant felspar is 

 of a basic species. This development of felspar in a limestone by contact 

 metamorphism is a point of considerable interest. The wollastonite occurs 



(1) Geologie Norwegens, 1880, p. 73. 



(2) Die silurischen Etagen, 2 und 3, 1882, p. 324. 



