PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 167 
ef the minerals zircon, epidote, sphene, rutile, microcline, and iron 
pyrites. 
In color these granites vary from very light to dark gray or nearly 
black, according to the amount and kind of mica or hornblende they 
contain, or from light pink to red, according to the color of the included 
orthoclase. In texture they vary from fine even-grained rocks, in which 
the various mineral ingredients are not easily distinguishable by the 
naked eye, to coarsely granular rocks, in which twin crystals of ortho- 
clase an inch or more in length are frequently seen. The quartz of 
these rocks never occurs in perfect crystals, but rather as crystalline 
grains filling the interspaces of the other minerals. As seen under the 
microscope in thin sections, it presents always a perfectly fresh and 
undecomposed appearance, and frequently contains numerous inclu- 
sions of small transparent crystals, the exact nature of which cannot 
be determined. In nearly every case it contains innumerable minute 
eavities or pores, some of which are empty while others contain the 
usual liquid and rapidly-moving bubble. 
In the majority of these granites orthoclase is the prevailing constit- 
tent, and not infrequently the one above all others to produce color and 
structural variations, as when in coarse, red crystals it gives color to the 
red granites of Calais, Jonesborough, and other localities; or as large 
snowy-white crystals, twinned after the Carlsbad law it produces the 
porphyritic structure so often seen in the granites of Mount Waldo and 
East Blue Hill. 
As seen under the microscope, the orthoclase always presents a more 
perfect crystalline form than the quartz, having evidently been the first to 
erystallize when the cooling process began, and hence its growth in any 
particular direction was less impeded. It is often quite turbid and 
epagne through decomposition, and included impurities, such as shreds 
of mica, hornblende, or opaque granules of unknown nature. When the 
hight is shut off from below the stage of the microscope, and the section 
viewed by reflected light only, it appears as a white, snowy mass, in 
strong contrast with the black, glassy surface of the quartz. The tri- 
clinic feldspars (microcline excepted) occur usually in smaller crystals 
than the orthoclase, and are much less opaque through impurities and 
decomposition. 
Hornblende, when present, is rarely in perfect crystals, but more often 
in imperfect and distorted forms, bearing numerous inclusions of biotite, 
apatite, and magnetite. In thin sections it varies from light yellow to 
deep green in color. 
The micas usually occur in irregular lamine, destitute of crystalline 
outline, though the muscovite is frequently met with in slender rhombic 
prisms, which are often inclosed in the orthoclase. Biotite is the more 
eommon mica in the Maine rocks, and in its unaltered state is of a 
smoky brown or yellow color in thin sections and strongly dichroic. 
Frequently, however, it is more or less altered into a greenish chloritic 
