124 THE GRANITES OF MAINE. 
Granite Company, which employed 1,400 men when filling large con- 
tracts. These quarries furnished material for the United States 
Treasury Department extension at Washington, the basement of the 
Charleston custom-house, the New York and Philadelphia post-offices, 
and the trimmings for the New York Metropolitan Museum of Art, 
Only an occasional block is now quarried. There is a wharf with 12 
i'e<>t of water at low tide. These quarries are referred to by J. E. 
Wolff in Tenth Census, vol. 10, 1888, pp. 119, L20, and by G. P. 
Merrill in Ann. Kept. Smithsonian Inst., pt. 2, 1889, p. 410. 
The granite (specimen 19, a) is a biotite granite of somewhat darl 
gray shade and of medium to coarse even-grained texture, with feld- 
spars up to one-half inch and numerous fine biotite scales rarel; 
exceeding one-tenth inch. It consists, in descending order of abun- 
dance, of delicate pink potash feldspar (orthoclase and niicrocline) 
smoky quartz, a very slightly bluish white soda-lime feldspar (oligo- 
clase), and black mica (biotite), together with accessory magnet ii 
and apatite. The oligoclase is partly altered to a white mica am 
rarely contains a little calcite. The biotite is here and there Inter! 
leaved with muscovite. The chief difference between this and the 
High Isle granite is that in this the biotite scales are generally 
smaller and much more abundant, which darkens the shade of (lie 
rock and diminishes the contrast between the minerals. 
Pock structure: The sheets are from 2 to 10 feet thick and dip 20° 
lo 10 S. in places. Heading- strike X. 80° E. and N. 35° \Y. 
The Sprucehead quarry is on Sprucehead Island, in the town of 
St. George, about 10 miles south of Rockland. Operator. Bod well 
Granite Company, Rockland, Me. 
The rock (specimen L0, a) is a quartz monzonite, with conspic- 
uous black and white particles and medium to coarse even -grained 
texture, consisting, in descending order of abundance, of translucent 
white soda-lime feldspar (oligoclase), milk-white potash feldspar 
(microcline), smoky quartz, black mica (biotite), and black horn- 
blende, together with accessory titanite, magnetite, pyrite, zircon, 
apatite, and secondary epidote. Zonal structure is common in the 
oligoclase. The contrasts between the black minerals, the smoky 
quartz, and the feldspars are very marked. 
The quarry is about 275 feet by 250 feet and has a maximum 
depth of 55 feet and an average depth of about 27 feet. Those parts 
of the quarry that lie below sea level require pumping. No strip- 
ping is necessary. 
Rock structure: The sheets, which range in thickness from less 
than a foot to 18 feet, lie horizontal or dip from 10° to 15° north- 
west and southwest, intersecting the surface*, which dips gently south- 
east. The sheets are irregular in thickness, owing to the tapering out 
of the lenses, but in general increase in thickness downward. Joints 
