LITHOLOGY. 197 
ite. It is instructive to note how generally in our granites the garnets 
are entirely without outer form, while in the vein granites and crystalline 
schists they are so often quite perfect. A section of the Antrim gran- 
ite, in which a garnet is included, is represented in Fig. 2 on Pl. xi. The 
_ form that the garnet takes seems to be entirely dependent on its surround- 
ings, and it encloses in its mass portions of both the biotite and quartz. 
The Antrim granite contains apatite in little hexagonal prisms, and also 
in numerous radiating groups of minute needles. Hornblende enters spar- 
ingly into the composition of the rock ; also, oligoclase, pyrite, and magne- 
tite. Excessively fine and very long needles of rutile pierce the quartz. 
But if, as has been shown, many of our granites retain traces of a 
stratified structure, which cause them to be referred to old sedimentary 
formations, in other places granite possesses the character of an erup- 
tive rock. The most remarkable occurrences of this nature are at 
Franconia and the Notch. At these points a light-colored biotite gran- 
ite occurs, and embedded in it are very numerous angular fragments of 
gneiss. Some of these fragments are small, some are very large; and 
thus there is formed an immense breccia, which cannot be represented 
in the cabinet on account of its great proportions.* This granite is 
called by Prof. Hitchcock the dveccta grantte. In the Notch, the point. 
where this granite occurs is regarded by Prof. Dana as the axis of an 
anticlinal, as proven by the arrangement of strata, and the large number. 
of granitic veins in the surrounding rocks. If, now, as suggested, gran- 
ite was once plastic, under the combined influence of heat and vertical 
and lateral pressure, it is easy to suppose that, when an upheaval took 
place, and the rocks were rent into a mass of broken fragments of the 
overlying strata, the underlying plastic mass might be forced, and being 
thus partially relieved from pressure, would solidify about the frag- 
ments, and form a breccia such as there exists, These breccias are 
certainly grand and interesting lithological examples, 
Many of the biotite granites are red, on account of the color which. 
oxide of iron imparts to the feldspar. One variety of the Conway gran- 
~ escounts ovr « €FCY peak in Stratford, are deep red; one from 
from Stark, possess a beautiful and delicate. 
ax Cause. Some. specimens of biotite granite are 
pete aie, een BSE 
* For figures, etc., see vol. ii, p, 169, of this report. 
