VEINS IN GRANITIC ROCK. 575 
tion of some schistose mineral: and although it may conform to the 
lamination of deposition in a metamorphic rock, this is not a neces- 
sary nor actual result under all circumstances. 
The objections derived from the large vein represented in figures 6, 
7, 8, will be found to lose part of their weight, when we consider the 
nature of the rock in which they occur, and the extent of the frac- 
tures and faults elsewhere indicated ;—that the veins of granite at Val- 
paraiso form a network throughout the rock, and are everywhere 
faulted and shifted in various oblique ways; and that the rock, a 
gneissoid granite, having but imperfect cleavage directions, would 
fracture in any way, though with some uniformity for the larger fis- 
sures, a uniformity which has been pointed out. In volcanic regions, 
the rocks are generally in layers, and the fissures are made a few ata 
time, or singly; and in granites intersected by trap dikes, the frac- 
tures are few and distant, showing by their comparative simplicity, 
even when most complex, that the rending the rock had undergone 
was simple in its character. But in the cliffs of Valparaiso, if there 
have been any fractures, the whole mass was broken in all directions, 
and the parts were made to shde upon one another very variously, 
some falling together again, and others opening irregularly. ‘The 
diminution of the vein at the intersection represented in figure 8, 
might be a result of gravity in the various parts around; the fissures 
would be diminished, enlarged, or entirely obliterated in this way, in 
different places, as the veins exemplify in their many irregularities. 
If, then, the smaller veins indicate fractures, their great number and 
various characters are such that the /arger veins should be of the very 
kind, as regards irregularity of size, that here exists. Their various 
subdivisions, separated by lines of micaceous gneiss, indicating seve- 
ral parallel fractures following one course, may have resulted from 
the rending action, (probably a lateral pressure and upturning,) which 
broke the rock so extensively, and smoothed, by rubbing together the 
surfaces of many fissures. Their direction was determined, like the 
direction of the larger veins, either by the structure of the rock, or 
the direction in which the force causing the fractures operated. The 
thinness of some of the seams, and the fact that they often appear as 
if they were only a variety of the granite which some cause had ren- 
dered more micaceous in lines, are the only objections to this explana- 
tion; and these, it seems, must give way before the other evidence. 
We here assume that the greater part of the granitic veins, as well 
as the faults, belong to one period. Of this we have probable evi- 
