VEINS IN GRANITIC ROCK. 577 
must have been, the epidote could not be the result of a sub- 
sequent ejection from below. The question, therefore, comes up, 
were they formed by ejections, liquid or gaseous, accompanying the 
ejection of the granite, or were they the result of a subsequent heat- 
ing of the rock, and some change by segregation along the lines of 
previous fracture or the walls of some of the granite veins? The 
inquiry also arises, how could a gneissoid granite become more mica- 
ceous and schistose adjoining an ejected vein, especially when this 
vein is more purely feldspathic than the rock either side? Epidote 
is not uncommon in the vicinity of trap dikes, where it has been 
formed by the action of the heat of the dike on iron, lime, silica and 
alumina, which ingredients are either all contained in the enclosing 
rock, or are derived in part from the heated trap. ‘Towards forming 
the mica and epidote, there is some magnetic iron disseminated in 
the gneissoid granite. But we forbear offering any farther conjec- 
tures with regard to the steps in the process. 
The objection to the view of ejection derived from the structure of 
the riband vein, is the only one yet unnoticed. It may be a result of 
segregation, similar in origin in some respects to concretionary nodules 
concentric in structure, but varied by the position of the material. 
Yet, possibly, this character has arisen like that of the dikes noticed 
on page 510; and the difference may be mainly due to that slow cool- 
ing which allowed, in the case before us, of the distinct crystallization 
of the material. 
Direction of lamination in the micaceous gneiss near or within veins. 
—The gneissoid granite has a schistose structure of its own, and this 
modifies, as figures 6, 7, 8, show, the direction of the laminated struc- 
ture in the micaceous gneiss. ‘This direction is farther modified by 
its relation to the positions of the two crossing veins of granite. ‘The 
following deductions in view of these points are derived from the facts : 
1. The micaceous gneiss enclosed within the veins, is laminated 
parallel with the direction of the vein. In this case the heat exerted 
its influence alike or nearly so on the two sides ; and the vertical axis 
of the crystals of mica is perpendicular to the source of heat. At the 
intersection of the veins, the larger vein gave the character to the 
lamination (figure 6). Also, where the veins are nearly equal, the di- 
rection of the lamination at the intersection in the included micaceous 
gneiss was determined by that vein (other things being equal) whose 
heat exerted the greatest influence. In figure 7, the lamination at the 
intersection is nearly in the line of @ or 0b, because a, 6, are nearer 
145 
