GNEISSES IN THE HIGHLANDS OF NEW JERSEY 



609 



essentially due to a plastic flow. Certain features of rupturing 

 likewise suggest that the attributes of a rigid body were retained 

 to some degree in such cases. Elsewhere, however, the phenomena 

 are more consistent with the idea of softening. The abrupt 

 flexures and general appearance of kneading of the material, as 

 well as the manner in which certain bands gradually fade out along 

 the strike, imply a partial fusion of the original material or a pene- 



FiG. 14 



tration of the magmatic liquor among the grains to such a degree 

 that their mutual adhesion was diminished and some freedom of 

 movement thus permitted. 



There can be little doubt that during the period of intrusion 

 the masses of rock now exposed were buried within the crust of 

 the earth to a depth at which the increase of temperature due to the 

 rise of the geotherms was considerable. In seeking an explanation 

 of the phenomena of intrusion the question arises whether the con- 

 ception which Sederholm^ has advocated to account for the relations 



^ J. J. Sederholm, Bulletin de la Conimis. Geol. de Finlande No. 23 (1907). 



