198 MINERALOGY AND LITHOLOGY. 
nearly black, on account of the preponderance of biotite. Such is a very 
handsome granite from Newcastle. 
A specimen of biotite granite from Franconia is somewhat remarkable, 
on account of the presence of fluor spar as one of its microscopic ingre- 
dients. A little hornblende is also present, which has a peculiar dichro- 
ism, being deep brown in one direction and dark blue in the other. 
A specimen from Whitefield is remarkable for its large amount of mag- 
netite. In it quartz largely predominates, and the mica is mostly in very 
minute grains. A specimen from Ossipee is remarkable for its large 
content of plagioclase and microcline, and which together outweigh in 
amount the orthoclase. It contains extremely long needles of rutile. 
Mica Hornblende Granites. Granites are numerous in which both mica 
and hornblende can be seen with the unaided eye, but the microscope 
enlarges this class widely. In some of the mica granites a bit of horn- 
blende is often found; but in those now to be mentioned the hornblende 
plays an important part. 
As typical of one class of these granites, a light-colored specimen from 
Colebrook may be described. In this granite, biotite and hornblende are 
most intimately mixed together. Sometimes one of the black spots that 
dot this granite will be seen under the microscope to be all of one or all 
of the other of these minerals, but more often of both. The two minerals 
are both very strongly dichroic, both being deep brown when the light 
passes in one direction, and deep yellow when it passes at right angles 
thereto. This rock contains considerable oligoclase. Apatite crystals 
of perfect form are quite common, and some epidote is present as a de- 
composition product. 
A number of handsome dark-colored granites, which are characterized 
by a kind of an olive-green color, are of this class. A specimen from 
Lightning mountain may be taken as typical, The rock is almost wholly 
composed of quartz and orthoclase, but the orthoclase is not of the white 
or colored opaque kind that is most common; it is the transparent 
variety that is called adularia. It has a very waxy lustre and a greenish 
tint, and imparts these characters to the rock. Under the microscope it 
is found to be much clearer, and more free from inclusions than our com- 
mon feldspar. The quartz is of a dark, smoky color, and only on close 
examination are grains of hornblende distinguished from it; but in thin 
