PETROGRAPHY. 355 



posed at the surface, they must have been subsequently elevated 

 to that position, and the superincumbent rocks have been re- 

 moved by denudation. Naumann supported the view that 

 most gneiss and crystalline schists represented the oldest 

 rock-sediments, but he agreed with Poulett-Scrope, Darwin, 

 Fournet, Cotta, and others that many gneisses had been pro- 

 duced by the deformation of eruptive rocks, and those might 

 be of different ages. A similar standpoint was afterwards taken 

 by Kjerulf and by Lehmann, the author of an excellent work 

 (1884) on the ancient crystalline schists, with special refer- 

 ence to the metamorphic rocks of the Erz mountains, Fichtel 

 mountains, the mountains of Saxony and of the Bavarian and 

 Bohemian frontiers. 



Delesse in 1861 declared himself an adherent of the meta- 

 morphic doctrines, and ascribed rock-metamorphism to high 

 temperature, water, pressure, and molecular movements. In his 

 opinion, after the first crust formed on the cooled surface of the 

 earth-magma, it was violently attacked by the action of the con- 

 densed vapours and afforded material for a great accumulation 

 of sediments. The metamorphism of these oldest sediments 

 produced gneiss and the crystalline schists, and these could 

 again become plastic and be transformed into plutonic rocks. 

 Thus Delesse assumed the deep-seated granite series to have 

 been produced by the re-melting and re-solidifying of meta- 

 morphosed sediments. He was supported in this view by 

 Daubree (1857). According to Daubree, the first-formed crust 

 was saturated with the water of the primitive ocean, and the 

 mineral constituents of gneiss and the oldest crystalline schists 

 separated out from a pulpy, softened mass. The younger schists 

 (chlorite schist, mica schist, phyllite) of the primaeval mountain- 

 systems were thought by Daubree to be pre-Cambrian deposits 

 metamorphosed by pressure and superheated water. The meta- 

 morphism of the younger Alpine schists was also referred by 

 Daubree to the same influences. 



Sterry Hunt similarly held that the crystalline schists re- 

 presented the earliest chemical deposits. He thought they 

 owed their planes of schistosity to the contemporaneous effect 

 of intense heat combined with the action of water and pressure. 

 He tried to elucidate the chemical processes of separation, 

 to determine an order of deposition, and even to demon- 

 strate that the eruptive rocks were also metamorphosed 

 sediments, which after having been made plastic penetrated 



