VEINS IN GRANITIC ROCK. 569 
The gneissoid granite adjoining a vein, sometimes changes to a 
well-characterized mica schist, or becomes a micaceous gneiss. And 
occasionally the direction of the layers conforms in part to the direc- 
tion of the vein. This fact is exhibited in figures 6, 7, 8, which 
represent sections of a vein along the shore nearly a fourth of a mile 
southwest of Valparaiso. Below or above the intersection, (sometimes 
both,) the lamine of the schist adjoining are curved to correspond 
with the angle of intersection ; and in other parts of the figures, only 
a tendency to the same structure is apparent. But when the vein is 
Fig. 8. 
one 
straight there is usually no conformity; yet a schistose structure is 
more distinctly developed alongside than is elsewhere apparent in 
the rock. ‘The character of the lamination is apparent in the figures. 
The veins when large, although entire in certain parts, become 
subdivided in others into several narrow portions, which continue on 
for a while, variously changing their size and course, and then reunite. 
The spaces between the strands often consist of mica schist or gneiss, 
like that adjoining the vein, and the schist is in general longitudinally 
laminated. In some places the mica schist is included in isolated 
masses, and from these there is a gradual transition to long parallel 
lines, which are sometimes broad, and either unbroken or interrupted 
at short intervals. These facts are shown in the figures referred to, 
in which the character of the rock is indicated. The limits of the 
two rocks, the feldspathic granite of the vein and the schist, are tole- 
rably well defined, though sometimes united by insensible gradations. 
143 
