ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 469 



igneous matter from beneath the broken crust. An analogous 

 phenomenon may every winter be observed on the St. Lawrence, 

 "When the ice shoves, pressure being exerted upon it from higher 

 up the stream, the floes of ice are raised upon their ends, and a 

 confused aggregate of inclined beds is the result ; and it is worthy 

 of remark that each of these beds is in itself distinctly stratified, 

 just as are the individual layers of the primary rocks, the cause of 

 this stratification being in each case not entirely dissimilar. 



We have thus endeavoured to remove Naumann's principal ob- 

 jections to the igneous origin of the primary stratified rocks. We 

 have next to refer to the objection founded on the mineralogical 

 composition of gneiss, which is the same as in the case of granite. 

 This objection is the presence in it of quartz, which occurs in such 

 a manner, as to indicate that it must have been the mineral which 

 solidified last of all, although it is the most infusible of the constit- 

 uents of granite. Perfectly well formed crystals of it often, it is 

 alleged, leave their impression on the adjoining feldspar and mica. 

 We have already seen that this vis denied by Sartorius von Wal- 

 tershausen, who also insists that the quartz formed subsequently to 

 the consolidation of the granite, by the action of water, must not 

 be confounded with the original granular quartz, which is never 

 or seldom found crystallized. In spite, however, of this denial, 

 many supporters of the igneous origin of granite consider it ne- 

 cessary to attempt to account for the occurrence of quartz in the 

 manner above stated. The following are the remarks of Naumann 

 on the subject : "Gaudin's experiments have shown that melted 

 silica becomes viscid before it solidifies, and while in this state it 

 may be drawn out into threads like sealing wax. This proves that 

 the temperature, at which it solidifies, lies very far below the tem- 

 perature, at which it fuses, wherefore this phenomenon has been 

 used by Fournet in support of his theory of the surfusion of silica, 

 the fundamental idea of which theory has also been strongly sup- 

 ported by Petzholdt (Fournet, Compte Rendu, tome xviii. 1844., p. 

 1050 ; and Petzholdt, Geologie, p. 313). Moreover Durocher has 

 pointed out that the fusing temperature of silica (perhaps amount- 

 ing to 2800 degrees C.) is not necessary in order to explain the 

 crystallization of granite, because the silica of the quartz formed 

 combined with the elements of the feldspar and the mica, a com- 

 pletely homogenous,igneous magma, in order to the fusion of which 

 atemperature approaching the fusing point of orthoclase may have 

 been sufficient. While the feldspar and mica crystallized from 



