RECENT RESEARCHES IN THERMAL META- 



MORPHISM. 



PART II. 



^* OME interesting instances of metamorphism in various 

 >^3 impure calcareous rocks (calc-mica-schists) have been 

 described by Weinschenk from the Venediger massif "in the 

 East Central Alps (19). The igneous intrusions that have 

 produced the transformations have been almost pure 

 pyroxene rocks, and are now represented by serpentine 

 rocks showing many features of interest. In contact with 

 the serpentine at the falls of the Islitz is an " omphacite- 

 like " rock consisting of tremolite, grey limestone, etc., with 

 infiltration of serpentine substance. This zone is some- 

 times several metres in width, and is succeeded by a com- 

 plex of crystalline silicate rocks, which sometimes recall 

 eclogites and allied types, and are true lime-silicate-hornfels 

 of various constitution. In part they are characterised 

 by garnet, but nearer to the contact epidote and diopside 

 occur instead, besides a blue amphibole and apparently a 

 plagioclase felspar. The garnets often show double refrac- 

 tion and zonary growth, a character frequently found in the 

 garnets of metamorphosed calcareous rocks in different 

 areas. In other localities described by Weinschenk the 

 metamorphosed calcareous schists have the character of 

 "epidote-hornfels " (with plagioclase, epidote, and actinolite), 

 " diopside-hornfels," etc. Whether these observations 

 throw any light on the origin of eclogites and similar rocks 

 may be doubted, since, as pointed out by Rosenbusch, the 

 typical eclogites of Central Europe agree in chemical com- 

 position with true igneous rocks. It is certain, however, from 

 observations in other districts, that the monoclinic pyroxenes 

 produced in thermal metamorphism include omphacites, i.e., 

 varieties rich in alumina and lime, as well as the non- 

 aluminous diopsides, etc. 



As already intimated, under the conditions which obtain 



