STRUCTURAL GEOLOGY. 23 



Genesis of the Arehean. The greenstones.] 



showing that trappean and other rocks in a heated and fluid state had been injected, 

 and Huttonianism prevailed largely. 



De la Beche (1837) urged a modified neptunian (Wernerian) hypothesis, viz.: 

 an unoxidized nucleus, a solid crust resting on a liquid interior, and a primeval 

 ocean, gradually settling from the atmosphere as the crust became cool enough; and 

 came to the conclusion that the stratified igneous rocks resulted from chemical 

 precipitation from such an ocean. These would be mingled, more or less, with the 

 products of direct igneous action, and often no lines of demarkation could be drawn 

 between them. 



Daubree (1860) adopted and amplified the view of De la Beche and enforced it 

 by experimental tests of crystallization of silicates under pressure in the presence of 

 the vapor of water. Daubree presumes that when the surface passed from the 

 dominion of fire to that of water, it experienced a long series of chemical conditions 

 promoting many decompositions and recompositions, aqueous action intervening 

 with igneous, and again giving way before it, during which two principal products 

 ist nirtim'si would be formed, one massive and the other sedimentary, passing into 

 each other gradually. The crystallization of the silicates must have taken place in 

 the presence of watery vapor. This vapor was under tension of 250 atmospheres, 

 and a temperature of about 1330 centigrade " about that of redness." Thus Daubree 

 adjusted the Wernerian hypothesis to the theory of La Place of a fused and cooling 

 globe, and supplied the "chaotic liquid," or universal ocean required by the 

 Wernerian hypothesis. 



In all these hypotheses the primeval rock is granite. Werner, Hutton, Mac- 

 culloch and Elie de Beaumont supposed the first crystalline rock to have been that 

 of granite, and Scrope imagined the whole earth to have separated from the sun as 

 an irregular, granitic aerolite, on which were subsequently formed the gneisses and 

 schists by the action of the primeval ocean, mainly through a process of disintegration 

 and of regeneration. The process of sedimentation for the gneisses and schists 

 though opposed by Saussure, was approved -by Hutton, Boue and Naumann, and 

 came to be generally believed. 



Hence, when Lyell (1833) proposed the theory of metamorphism, giving origin 

 to the hypogene metamorphic rocks (gneisses and schists) by a deep-seated change in 

 the detritus from the first granitic crust, it was readily accepted, and has remained 

 in vogue to the present time. 



This theory, however, as it requires the destruction of a vast amount of the 

 original granitic subcrust in order to form the 30,000 feet, more or less, of the gneisses 

 and schists, met with a physical difficulty. It requires at once sufficient elevation of 

 the granitic crust to bring it into contact with erosive agents, and a submergence 



