186 SCIENCE PROGRESS. 



internal heat of the earth, and thermal metamorphism thus 

 produced on a regional scale. Further, the mechanical 

 generation of heat in connection with crust-movements 

 must give rise to phenomena of thermal metamorphism, 

 which we may expect to find often complicated by purely 

 dynamic effects. 



In this country a considerable amount of study has been 

 devoted to thermal metamorphism in the last twenty years, 

 the lead being taken by Allport in Cornwall, and Clifton 

 Ward in the Lake District. Among more recent contribu- 

 tions may be mentioned those of Miss Gardiner (i) on the 

 New Galloway district, Barrow (2) on the South-eastern 

 Highlands of Scotland, and Harker and Marr (3) on the 

 rocks surrounding the Shap granite. On the continent 

 Rosenbusch has rendered classic the district of the Steiger 

 Schiefer in the Vosges, Lossen the Harz Mountains, Brog- 

 ger and afterwards Lang the neighbourhood of Christiania, 

 and Barrois the west of Brittany. As preliminary to some 

 more general remarks on thermal metamorphism, I select 

 some recent researches in Saxony, which illustrate charac- 

 teristic phenomena in rocks belonging to various lithological 

 types, and are worthy of being better known by English 

 geologists. 



The metamorphism produced by the intrusion of the 

 great mass of the Meissen syenite was described by the 

 officers of the Saxon Geological Survey a few years ago. 

 Some of the features, as noticed by Sauer (4) in the memoir 

 accompanying sheet 48 of the map, are well worthy of 

 notice. The aureole of metamorphism has a breadth of 

 about two kilometers, or in places where the syenite under- 

 lies the strata at a low angle as much as four kilometers. 

 The rocks affected belong to the Ordovician and Silurian 

 formations. They are for the most part ordinary clay-slates 

 with disseminated carbonaceous matter ; but these some- 

 times pass, on the one hand, into fine-grained siliceous slates 

 (Kieselschiefer and Adinolschiefer), and, on the other hand, 

 into bands of greywacke and beds of quartzite. There are 

 also basic volcanic rocks ("diabase-tuffs" and "diabases"), 

 and, associated with these, beds of pure limestone. 



