Ixvi PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [May I9OI, 



and Leonhardt clearly recognized the great natural group of f rag- 

 mental rocks ; but the true limits of the other equally natural 

 groups were, so far as general treatises are concerned, brought into 

 prominence for the first time in the work by Yon Cotta, the 

 English translation of which appeared in 1866. 



Progeess during the Pirst Half of the Century. 



Igneous rocks played but a small part in the Wernerian system. 

 They were regarded as stratified rocks melted by heat, due to the 

 burning of coal beneath volcanic districts. We now recognize that 

 they are of great importance, and probably represent the original 

 source of all the other rocks. The clearing up of our ideas as 

 to their nature and mode of origin centres round two controversies : 

 one as to the origin of basalt, the other as to the origin of 

 granite. 



It is difficult for us to realize the condition of things which 

 prevailed during the early years of the century, when the martial 

 spirit of the age seems to have affected the scientific world, and a 

 furious controversy raged between the iS'eptunists and the Vulcanists 

 as to the origin of basalt. We look with a feeling of astonishment 

 at the controversialists, condemn their methods, and admire the 

 calm figure of the old man Desmarest as he sits there refusing to 

 be dragged into the controversy, and quietly replies to his chal- 

 lengers ' Go and see.' Now and again, in looking through some 

 neglected cabinets of our museums we come across dust-covered 

 specimens labelled ' Ammonites in Basalt from Portrush,' and are 

 thus forcibly reminded of those stirring times. 



The controversy as to the origin of granite lasted longer, and 

 during its later stages, at any rate, was conducted with dignity and 

 a due regard to the amenities of scientific discussion. It resulted, 

 moreover, in a very decided enlargement of our conceptions as to 

 subterranean phenomena. The Wernerian view that granite was a 

 precipitate from a primordial ocean was compelled to give way as 

 soon as the tectonic relations of granitic masses, so well described 

 by Hutton, Playfair, and Sir James Hall, were clearly realized. The 

 phenomena of granite-veins, the occurrence of inclusions of the 

 surrounding rocks, and the sharpness of the junctions between granite 

 and the strata with which it is in contact, prove beyond all doubt 

 that the material of which many granite-masses are composed must 

 have been intruded from below in a plastic state. Towards the 



