296 science progress. 



a decrease in the proportions of silica (from 63 to 40 per 

 cent.) and of alkalies and an increase in the proportions of 

 alumina and iron oxides. The author does not assume that 

 the rocks analysed were before metamorphism of identical 

 composition, but making allowance for original differences, 

 he claims that there has been a loss of certain ingredients 

 or an addition of others. It is clear, however, that such 

 rocks as mica-schists are not suitable for a strict inquiry on 

 this point : we require rocks in which an individual bed can 

 be followed into the metamorphic aureole, so that the 

 material studied may be fairly assumed to have been of 

 uniform character before metamorphism. The same objec- 

 tion applies to the conclusions which Hawes at an earlier 

 date drew from the metamorphosed mica-schists near the 

 Albany granite. 



Some curious observations were made by Williams 

 upon inclusions of highly metamorphosed schist in the mass 

 of the intrusive diorite. Of these some consist mainly of 

 pleonaste and corundum, with some magnetite, biotite, and 

 felspar ; others are essentially of quartz grains with various 

 accessory minerals ; others of staurolite and ripidolite with 

 more or less sillimanite ; and others again largely of flakes 

 of margarite with varying amounts of other minerals. The 

 phenomena bear a close resemblance to those seen in the 

 neighbourhood of Klausen in the Tyrol, and the remarkable 

 mineral aggregates constituting the inclusions are also paral- 

 leled by the included patches in the kersantite of Michael- 

 stein in the Harz, described by Koch (24). The occurrence 

 of minerals very rich in alumina, such as pleonaste and 

 even corundum, is a curious feature in all the three dis- 

 tricts. 



An exhaustive memoir by Salomon deals with the 

 thermal metamorphism of various crystalline schistose rocks 

 in the Adamello range, between Italy and the Tyrol (25). 

 The intruded rock which causes these transformations is the 

 well-known "tonalite". Certain phyllites in the earlier 

 stage of metamorphism show especially the production of 

 brown biotite ; nearer to the contact they pass into a 

 schistose andalusite-mica rock consisting of muscovite, 



