LITHOLOGV. . 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 breccia granite. 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- 

 ite, and a granite from Percy peak in Stratford, are deep red ; one from 

 Twin mountain, and one from Stark, possess a beautiful and delicate 

 pink tint, from the same cause. Some specimens of biotite granite are 



* For figures, etc., see vol. ii, p. i6g, of this report. 



