Geology ; as illustrated by Chemistry and Physics. 49 



Quartz has never yet been found in a lava, or in any vol- 

 canic product immediately after the solidification, as a sepa- 

 rate and not accidentally enclosed constituent. Such a fact 

 could only have been overlooked by a volcanic zeal running 

 wide of all physical and chemical laws. It was not until 

 long after the hypothesis of the igneous origin of granite 

 had been regarded as established, that some of the more 

 moderate Plutonists were found to direct attention to this 

 circumstance, and to admit that it could not be brought into 

 harmony with the plutonic origin of granite, without, how- 

 ever, renouncing the general hypothesis. 



The Plutonists found abundant occupation in explaining 

 the formation of gneiss, a rock which, like granite, consists 

 of quartz, feldspar, and mica, but differs essentially from it 

 in possessing an evident stratification. The constituents 

 of gneiss, then, speak in favour of a pyrogenous formation ; 

 according to the views of the Plutonists, its stratification 

 indicates that it is a deposit from the sea. This contradic- 

 tion separated the Plutonists into two different parties. The 

 one consisted of those who did not question the sedimentary 

 origin of gneiss but assumed a subsequent metamorphosis 

 into crystalline rock to have been effected by igneous agency. 

 The cause of this igneous metamorphosis they could not find 

 in the Pidimentary rocks themselves, but were compelled to 

 seek for them in the adjoining rocks. This led to the hypo- 

 thesis of plutonic metamorphism, according to which an 

 amorphous sedimentary rock is supposed to be heated by 

 contact with a melted mass ascending from the interior of 

 the earth, and then to acquire a crystalline texture during 

 the gradual cooling. 



The other party consisted of those geologists who con- 

 sidered that the stratification and parallel structure of gneiss, 

 and other stratified crystalline rocks, furnished no reasons for 

 regarding them as other than pyrogenous formations, since 

 their phenomena are equally marked in some lavas.* These 

 views are opposed to all the evidence which exists against 



* Naumann, Geognosie, p. 741. 

 VOL. LI II. NO. CV\— JULY 1852. D 



