RESEARCHES IN THERMAL METAMORPHISM. 187 



The clay-slates and cleaved greywackes are converted 

 in the neighbourhood of the intrusion into rocks composed 

 chiefly of andalusite, biotite, and quartz, with or without a 

 schistose character, or into sillimanite-bearing quartz-biotite- 

 schists. The andalusite, in crystals up to 1 cm. long, is 

 very abundant, and, as usual, crowded with inclusions of 

 other minerals, such as quartz, biotite, and magnetite. 

 Muscovite and felspar have also been formed, and of these 

 too the larger crystals are full of inclusions. The sillimanite 

 occurs in the usual crowded aggregates of needles, but it is 

 curious that these occur even more in the biotite-flakes than 

 in the quartz. The minute rutile-needles, which are abun- 

 dant in the original clay-slates, have disappeared in the 

 metamorphism, the titanic acid being taken up by the new- 

 formed biotite. 



Outside the zone of most highly altered rocks is a zone 

 of " knotted " or ''spotted" mica-schists (Knotenglimmer- 

 schiefer), and a point of special interest is the discovery 

 that in a large part of these rocks the " knots " are really 

 crystals of cordierite. In the siliceous and alum-slates, 

 which in their original state contained a quantity of free 

 hydrous silicate of alumina, the alteration extends to a 

 greater distance from the syenite, the characteristic pro- 

 duct being chiastolite in crystals 1 cm. long. 



The adinole-like rocks are metamorphosed into quartzite- 

 schists. and the original quartzites appear to have been 

 recrystallised near the intrusion. The quartz in the meta- 

 morphosed rocks is free from fluid-pores. 



The basic tuffs have o-iven rise to hornblende-schists 

 and especially anthophyllite-schists, the augite and its de- 

 composition-products being converted into hornblende or 

 actinolite or to a great extent into the rhombic amphibole 

 anthophyllite, while the felspars are recrystallised. The 

 associated limestones, originally fine-textured to compact, 

 become usually rather coarse-grained marbles ; but the thin- 

 bedded alternations of limestone with tuff give rise in the 

 immediate neighbourhood of the syenite to more complex 

 mineral-aggregates similar to those well known at Monzoni 

 in the Tyrol. The minerals produced include garnet, ido- 



