BLACK GKANITES. 61 
certain Scotch gabbros, but in them the banding was also contorted 
prior to crystallization. 
Dikes. — The Addison gabbro is traversed by whitish dikes of fine- 
grained quartz monzonite, from 1 to 14 inches thick. (See PL X, .1.) 
They have a border, from one-twentieth to three-fourth inch thick, 
of coarser material, in which the particles measure up to one-tenth 
inch in diameter. The constituent minerals, in descending order of 
abundance, are soda-lime feldspar (oligoclase-andesine), potash feld- 
spar (orthoclase) in slightly less amount, clear quartz, biotite, and 
hornblende, together with accessory magnetite, titanite, and apatite. 
The texture of this dike rock differs from that of any of the aplite 
dikes examined from the granite quarries in that the soda-lime feld- 
spar is mostly in lath-shaped crystals (0.37 by 0.07-0.11 mm.), al- 
though occasionally also in squarish forms, and makes up an irregular 
network, the meshes of which are filled with quartz. 
In the mica-quartz diorite of the Beaver Lake ( uarry, near Red- 
beach (p. 164), there is a dike of grayish pinkish aplite, from 4 to 8 
inches wide, which appears to be more recent than a neighboring 
dike of olivine basalt, as its branches cross it. The particles in this 
aplite range from 0.11 to 0.01 mm., averaging roughly about 0.30 
mm., and consist of soda-lime feldspar (oligoclase), much less potash 
feldspar, quartz, and biotite. The aplite is thus a biotite granite. 
Dikes of pegmatite and also of aplite traverse the Round Pond 
(Lincoln County) quartz diorite (see Pis. X, B, and XI, A), and 
pegmatites penetrate the overlying sedimentary schists. Miss Bas- 
com has described some schists and pegmatites from points in Johns 
Bay, about 8 miles south-southwest of Round Pond, which are prob- 
ably of the same age. 6 It is uncertain whether the lenses and dikes of 
pegmatite in the schists were formed prior to the veins in the diorite. 
The quartz diorite of Round Pond (Lincoln County) is also 
traversed by a diabase dike, w T hich also crosses one of the pegmatite 
dikes and is therefore of later date. (See PI. XI, .1.) The mica- 
quartz diorite of Beaver Lake, near Redbeach, in Washington County, 
is traversed by a dike of olivine basalt, a very fine-grained black 
rock consisting of needlelike crystals of feldspar (andesine-labra- 
dorite) with pyroxene, olivine, and magnetite, together with acces- 
sory biotite and a white mica. 
Contorts. — The only contact of black granite with other rocks Avell 
exposed at the quarries visited in the preparation of this report is at 
the Round Pond quarry. (Peter Svensen & Co., p. 139.) This has 
See Geikie, after Teall, op. eit., p. 25G. 
h Bascom, Florence. On some dikes in the vicinity of Johns Bay, Maine: Am. Geologist, 
vol. 23, 1899, pp. 275-280, Pis. IX. X. XI. See also in this connection: Lord, E. C, 
Notes on the geology and petrography of Monhegan Island, Maine : Am. Geologist, vol. I'd 
1900, pp. 329-347. 
