352 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



any difference of opinion regarding the derivation of the rock- 

 material composing stratified deposits on the one hand from 

 the fragmented and finely triturated products of surface denuda- 

 tion or from the chemical activities of infiltrating water in the 

 crust, and on the other, from the accumulation of organic de- 

 posits. But the origin of gneisses and the crystalline schists is 

 still shrouded in mystery; much is known, but far more remains 

 to be discovered. These rocks used to be regarded as the 

 fundamental rock-formation of the sedimentary succession ; 

 the lowest member of the group being usually gneiss or coarsely 

 foliated and banded granitic rock, and the uppermost usually 

 phyllite or finely foliated lustrous, slaty rock. In the eighteenth 

 century, three leading hypotheses were promulgated in explana- 

 tion of the origin of these rocks. One theory (supported by 

 Buffon, Breislak, and others) regarded the gneisses and the 

 crystalline schists as the fundamental rocks of the earth's crust, 

 the product of the first consolidation of molten rock material 

 on the cooling surface of the earth ; the Wernerian theory 

 represented them as the oldest chemical precipitates from the 

 primaeval aqueous envelope of the earth, possessing a crystalline 

 texture in virtue of the high temperature at the earth's surface 

 in the primaeval epoch ; Hutton regarded them as normal 

 sedimentary deposits, not necessarily of the primaeval epoch, 

 which had been carried to greater depths in the crust after 

 their deposition, and there been melted, metamorphosed, and 

 rendered crystalline by the combined influence of the earth's 

 internal heat and enormous crust-pressure. In his concep- 

 tion of the relation of dynamic agencies to rock-deformation, 

 Hutton was far ahead of his contemporaries, and the 

 nineteenth century was well advanced before Darwin, Poulett- 

 Scrope, Sharpe, and a few of the keenest observers began to 

 apply the principle of dynamic agencies of deformation in the 

 earth's crust. Beroldingen explained gneiss as regenerated 

 granite. Although with certain modifications, each of these 

 hypotheses claims supporters at the present day. 



In 1822 Ami Boue, in his geognostic description of Scotland, 

 modified the Huttonian hypothesis in so far as he thought that 

 in addition to subterranean heat and pressure, the action of 

 vapours and gases had played a part in the metamorphosis of 

 sedimentary deposits to crystalline rock. The Norwegian 

 geologist. Keilhau, in the following year advanced his view 

 that a foliated structure had been superinduced upon crystal- 



