"BATHOLITHS" OF HALI BURTON -BAN CROFT AREA 789 



the center of the gneissic areas, where, it would seem, by Adams' 

 theory, that the pure gneiss of the intruding batholith should be 

 found. 



This fact makes it easy to believe that the granite was intruded 

 along planes of slight resistance, and that the limestone terrane 

 of the Grenville series became an immense steam pack, at the time 

 of the intrusion of the granite, with layers of gases followed by 

 fluid granite alternating with layers of limestone. The pre- 

 Cambrian granites were probably accompanied by an immense 

 amount of pneumatolytic gases. The loss of these gases at higher 

 levels due to decreasing pressures accounts for the gradual lessening 

 of the interaction of granite and limestone away from the main 

 granite mass, while within the gneissic areas the retention of the 

 gases allowed the granite to effect a complete change of the lime- 

 stone to gray gneiss and amphibolite. At certain places the granite 

 failed to penetrate great lenses of the limestone. The gases from 

 layers of fluid magma at the top and bottom of these lenses meta- 

 morphosed their borders but failed to affect their centers. Lenses 

 of pure limestone were, therefore, preserved in the midst of gray 

 gneiss and amphibolite. 



It has been inferred that the intrusion of the granite occurred 

 along planes of weakness. These, as the structure now shows, 

 were parallel to the stratification of the limestones. Daly and 

 Dawson have stated that in the Shuswap area these planes were 

 due to static metamorphism. Fissility produced in this way would 

 be less apparent in limestones than in the quartzose rocks of British 

 Columbia. However, the fact that the gneissic structure of the 

 Laurentian gneiss is parallel to the stratification of the Grenville 

 series would favor the view that the granite solidified under condi- 

 tions of stress similar to those which produced the parting planes 

 along which it was intruded. A vertical dike near Baptiste Lake, 

 west of Bancroft, Ontario, shows horizontal schistose structure 

 similar to certain dikes described by Daly 1 in the Shuswap area. 

 Adams and Barlow 2 ascribed the gneissic structure of the Laurentian 

 gneisses to the pressure of intrusion of the granite magma. This, 



1 Cf. to figure in Guide Book No. 8, Part II, Internat. Geol. Cong., Can (1913), 130. 



2 Can. Geol. Surv., Memoir No. 6 (1910), 78-81. 



