360 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



extensive district of regional metamorphism in the north-west 

 of Scotland had meantime been brilliantly elucidated by 

 Professor Lapworth. Messrs. Peach and Home, together with 

 other members of the Geological Survey, were continuing the 

 work of mapping and research in the new light that had been 

 thrown on the problem by Lapworth's demonstration of the 

 great crust-movements of overthrust, and the associated meta- 

 morphism of portions of the Cambro-Silurian deposits. It 

 was securely determined in that district of regional metamor- 

 phism that there was fundamental gneiss at the base of the 

 whole sedimentary succession, and also metamorphic gneiss 

 representing sedimentary rocks of the oldest Palaeozoic epochs 

 which had been locally altered during the gigantic crust-move- 

 ments. The altered and unaltered deposits dovetailed into 

 one another with complicated stratigraphical relations. 



The conclusive results of the work done in the north-west 

 Highlands of Scotland were of the highest importance for the 

 general questions in dispute regarding the causes and processes 

 of metamorphism. In more recent years, Mr. Barrow has 

 shown the presence of eruptive bosses of gneiss as well as of 

 granite, and has traced numerous veins of pegmatite passing 

 from these bosses into the group of crystalline schists. 



The last fifteen years of the nineteenth century witnessed 

 very great advances in our knowledge of rock-deformation 

 and metamorphism. It has been found that there is no 

 geological epoch whose sedimentary deposits have been 

 wholly safeguarded from metamorphic changes, and as this 

 broad fact has come to be realised, it has proved most un- 

 settling and has necessitated a revision of the stratigraphy of 

 many districts in the light of the new possibilities. The 

 newer researches scarcely recognise any theory ; they are 

 directed rather to the empirical method of obtaining all possible 

 information regarding microscopic and field evidences of the 

 passage from metamorphic to igneous rocks, and from meta- 

 morphic to sedimentary rocks. The present views held by 

 the leading German petrographers, Rosenbusch and Zirkel, 

 may be in conclusion shortly indicated, as they will give a 

 fair representation of the existing progressive and conservative 

 tendencies regarding the difficult questions of pressure-meta- 

 morphism. 



Rosenbusch has strongly advocated the origin of the crystal- 

 line schists through dynamo -metamorphic agencies. In a 



