168 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 
product, when its dichroic properties are greatly lessened. It bears 
numerous inclosures of apatite and magnetite. 
Apatite, which is present more or less in nearly all the granites and 
gneisses, occurs nearly always in minute colorless hexagonal prisms, fre- 
quently inclosed in the mica or hornblende, and showing usually one 
or more lines of fracture at right angles with their length. Epidote 
appears either as minute colorless perfect crystals or as larger irregu- 
lar grains of a faint greenish color, and slightly pleochroic, as is seen im 
the hornblendic granite of Mount Desert. Zircons occur rather sparingly 
in many of these granites in the form of square prisms, too minute to 
allow an accurate determination.of their optical properties, but never- 
theless easily recognizable by their strong relief and peculiar iridescent 
polarization colors. | 
Magnetite is present, so far as observed, in all the Maine granites, 
occurring as small opaque grains, often without crystalline form, or again 
in small perfect octahedrons. It is usually present only in microscopic 
proportions, though occasionally in sufficient abundance to be visible 
to the unaided eye as opaque lusterless grains on a polished surface. 
It is found in greatest abundance in those rocks which bear hornblende 
or biotite as their characterizing accessory, while in those in which 
muscovite is a prevailing constituent it is almost entirely lacking. In 
but few of the rocks examined does iron pyrites occur in sufficient quan- 
tity to be of any practical importance. It can ordinarily be seen only 
with the microscope, though ocecasionaily visible to the naked eye as 
small glistening brassy-yellow specks on a broken surface of the stone. 
Sphene is a very common accessory in many of the Maine granites, 
occurring usually as small grayish rounded or irregular grains without 
crystalline form, though occasionally the characteristic wedge-shaped 
crystals are seen. It is but faintly pleochroic, and polarizes in dull 
colors. 
Biotite granite.—The great majority of the Maine granites are of this 
kind. They vary usually from light to dark gray in color, though pink- 
ish and red varieties are quarried in a few instances. At Red Beach, 
near Calais, there is quarried a coarse reddish rock, very compact a 
hard, which from a simple examination with the unaided eye is seen to 
be composed of coarse red orthoclase, a nearly white or cream-colored 
plagioclase, smoky quartz, and.a few small shreds of mica. An exami- 
nation of a thin section with the microscope does not greatly increase 
the number of constituent minerals. The feldspars are seen to be quite 
opaque, as is the case with all the red granites, and the quartz is quite 
free from the minute colorless inclusions above referred to. The mica, 
which is usually of a greenish color, in thin sections, is very evenly 
disseminated throughout the rock and in very small shreds, bearing 
numerous inclosures of magnetite. A few small apatite crystals are as 
usual present. The rock is quite poor in plagioclase. This beautiful 
rock is fully equal if not superior in beauty and durability to much of 
