124 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



subsequently more or less altered, sometimes even fused and 

 rendered glassy or slaggy. 



When, after Werner's death, his two most famous pupils, 

 Leopold von Buch and Alexander von Humboldt, declared 

 themselves in favour of the volcanic origin of basalt, the 

 defeat of the strict Neptunists was sealed. A historical account 

 of the whole question of basalt, and the disputes between 

 Neptunists and Volcanists, may be read in Keferstein's 

 Contributions to the History and Knowledge of Basalt (1819). 



But Neptunian doctrines still continued to be accredited for 

 granite, syenite, gneiss, and other members of the holo- 

 crystalline series. Descartes, Leibnitz, and Buffon had cer- 

 tainly explained the primitive earth-crust as the result of 

 cooling from a molten mass, but they had made no attempt 

 to explain the origin of the various kinds of primitive rock. 

 It was generally supposed that granite, gneiss, schist, porphyry, 

 phonolite, and similar rocks were chemical precipitates separated 

 from a primitive ocean strongly impregnated with mineral sub- 

 stances. Therefore Von Fichtel, writing in the end of the 

 eighteenth century, showed an exceptionally enlightened spirit 

 among German geologists when he included not only basalt 

 but all granitoid, gneissose, schistose, and doleritic series as 

 igneous in their origin. Fichtel distinguished two kinds of 

 volcanic mountains (a) those which consist of immense 

 uniform masses, sometimes building up a whole mountain- 

 ' chain, and (b] those in which rocks of different constitution 

 alternate with one another in a stratified way (lava, ashes, 

 rapilli, etc.). He described the homogeneous masses as having 

 risen without any violent phenomena of eruption, and having 

 penetrated the crust at the places of least resistance ; whereas 

 the others were produced by successive eruptions, during which 

 the ejected material gathered in conical form round the craters 

 of eruption. 



But the great founder of the Plutonic school was James 

 Hutton. According to Hutton, heat is the most powerful 

 agent in the origin of rocks. The heat that pervades the lower 

 horizons of the crust converts all rock-material into a molten 

 magma. Under the superincumbent weight of the younger 

 sedimentary rocks and the ocean, mineralogical combinations 

 can take place which would not be possible at the surface 

 under conditions of normal pressure and rapid cooling. The 

 primitive schists and limestones have been produced from a 



