344 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



(slate, greywacke), as well as the interbedding of granite with 

 gneiss and sedimentary schists, led Bischof to agree with the 

 opinion of Keilhau (1825) and Virlet d'Aoust (1846), that 

 granite and syenite represented altered clay slates. Diabase 

 and even" melaphyre and basalt were regarded by Bischof as 

 shales and clays, poor in silica, and altered by the agency of 

 water. 



C. W. C. Fuchs, in 1862, supported Bischof's views in a 

 valuable treatise on the mineralogical and chemical consti- 

 tution of the granite in the Harz mountains. He regarded 

 the granite as a product of the alteration of sedimentary grey- 

 wacke by means of water, hornstone being formed in the 

 earlier phases of alteration, and granite during the later 

 phases; these two rocks were connected by a transitional 

 series of alteration products. 



A serious objection to the pyrogenetic origin of granite was 

 advanced by H. Rose in 1859. He showed that after fusion 

 quartz passes into an amorphous modification of silica, thereby 

 changing its specific gravity from 2.6 to 2.2. As the quartz in 

 granite and granitoid rocks always has a specific gravity of 

 2.6, it seemed impossible to suppose it had merely separated 

 from a dry fused mass. 



The aquo-igneous origin of granite suggested by Scheerer 

 on theoretical grounds was soon to receive an experimental 

 conformation. Struck by the peculiar changes which sedi- 

 mentary deposits underwent in contact with, or in the near 

 vicinity of, eruptive rocks, Professor Daubree attempted to 

 show that neither heat alone, as Hutton had supposed, nor 

 vapours and gases would suffice to call forth these changes, 

 but that superheated water under great pressure was the most 

 important agent in the metamorphism of rocks. To prove this 

 hypothesis, Daubree in 1857 conducted a series of very 

 instructive experiments. A glass tube partially filled with 

 water, and hermetically sealed at both ends, was placed in a 

 strong iron tube, which was then closed and exposed to a 

 temperature slightly below red heat. After a few days the 

 glass tube was attacked ; in parts of it a finely laminated 

 structure was induced, and the whole tube was transformed 

 into a zeolitic mineral, in virtue of the removal of silica, alumina 

 and soda, and the addition of water. Innumerable small crystals 

 of quartz formed; microlites and diopside crystallites developed 

 in abundance in the less violently attacked parts of the tube, 



