PROCEEDINGS OF UNITED STATES. NATIONAL MUSEUM. 175 
flakes. In external appearance this rock is very much like the coarser 
varieties of the Biddeford granite. 
Muscovite biotite granites.—The granite of Augusta and Hallowell has. 
long been justly celebrated for its beauty and fine working qualities. It 
is a fine, light-gray rock, the uniformity of whose texture is often broken 
by the presence of large white crystals of microcline, which inclose 
small, rounded grains of quartz. Biotite and muscovite occur in abun. 
dance, and in about equal proportions, but in small flakes, the muscovite 
appearing as small, silvery-white, glistening particles on a broken sur- 
face of the rock. Under the microscope three feldspars are readily dis- 
tinguished—orthoclase in imperfect crystals and irregular grains, an 
abundance of plagioclase, and microcline in large plates filled with cay- 
ities and inclosures of muscovite and quartz. In the thin sections the 
quartz inclosures are usually circular in outline and are pierced in every 
directiou by minute, thread-like crystals of rutile, in polarized light 
showing up in strong contrast with the beautiful basket-work structure 
of the inclosing microcline. All the feldspars are quite fresh and pure. 
The quartz is in small, irregular grains, containing but few cavities, but 
innumerable threads of rutile. The biotite occurs in small shreds, with- 
out any attempt at crystalline form, while the muscovite, although 
usually in larger, irregular lamine, is also sometimes found in small, 
perfect, rhombic prisms. A few apatite crystals are present, together 
with occasional garnets, which in thin sections are always destitute of 
crystalline form, appearing as rounded or oval nearly colorless bodies 
traversed by many irregular lines of fracture. They are quite free from 
impurities, though occasionally containing inclosures of biotite. As 
is usual in muscovite-bearing rocks but little magnetite is present; i 
two cases only grains of pyrite were noticed. 
This is one of the best working of the Maine granites, and is used 
very extensively, not only for building and monuments, but is carved 
into statues like marble. The rock is properly a gneiss, but showing 
no signs of stratification in the hand specimen is classed here as a granite. 
As illustrative of the great extent of the quarries, it is stated that blocks 
200 feet in length, by 40 feet in width and 8 feet in thickness, can be 
broken out in a single piece if so desired. 
The rock quarried at North Jay is practically identical with that of 
Hallowell, and need not be further noticed here. The Lincoinville rock 
is a trifle darker, but otherwise appears nearly the same. All closely 
resemble the well-known granite of Concord, N. H. 
GNEISS. 
The composition of gneiss is identical with that of granite, from which 
it differs only in structural modifications, its characterizing feature being 
that it possesses a laminated or stratified appearance due to the arrange- 
ment of the individual crystals constituting the accessory minerals (mica 
and hornblende). It is therefore scarcely necessary to go into a special 
