GNEISSES IN THE HIGHLANDS OF NEW JERSEY 699 



doctrines have evidently had in mind their appHcation to a certain 

 t)^e of phenomenon and do not imply that all granitic intrusions 

 have occurred under like conditions or been accompanied by similar 

 effects. It seems to be considered at times that the observations 

 of Lacroix in the Pyrenees are opposed by those of Brogger in the 

 Christiania region, but these two geologists themselves evidently 

 perceived that they had to do with processes of a different nature 

 and that the same phenomena should not be sought or the same 

 explanation applied. Lacroix^ has discussed Brogger's views and 

 says: ''None of the arguments which this scientist deduces from 

 the study of his region bears against the theory of assimilation, 

 applied to the Haute-Ariege ; the facts which he has described are 

 in effect the antithesis of those which I have set forth in this memoir." 

 He suggests that the dissimilarities may be attributed to differences 

 in the depth at which the intrusions took place in the two regions. 



Brogger^ also states that it would not be justifiable with- 

 out further evidence to apply his observations on the Christi- 

 ania district to the granite regions of the older primitive rocks 

 and regionally metamorphosed fold-mountains. Evidently both 

 Lacroix and Brogger recognize the fact that the type of granitic 

 intrusion to which each has devoted his attention is not the only 

 form which is found. 



The relations which Michel-Levy, Lacroix, Sederholm, and 

 others have described offer an array of evidence in confirmation 

 of their views, and there seems to be no inherent obstacle to accept- 

 ing them. 



In trying to account for the formation of a dilute magmatic 

 solution in advance of the main invasion several possibilities sug- 

 gest themselves. 



It appears probable that the escape of volatile constituents 

 through pores of the wall-rock too minute in size to permit un- 

 changed magma to follow would have a tendency in this direction. 

 Field evidence appears to warrant the view that considerable 

 quantities of vapors have often escaped in this manner and that 



' A. Lacroix, "Le granite des Pyrenees et ses phenomenes de contact," Carte geol. 

 de France, No. 64 (1898), p. 63. 



=" W. C. Brogger, Die Eruptivgesteine des Christiania-Gebietes, II (1895), 152. 



