48 THE GRANITES OF MAINE. 
Most of these dikes are so firmly welded to the granite that hand 
specimens that are one-half granite and one-half diabase are readily 
obtained. Thin sections of the glassy rims of dikes at Bryant Pond 
and Fryeburg show that the dike sent out microscopic branches for 
short distances into the granite, in places surrounding some of its 
quartz particles. A dike at the Dunbar Brothers' quarry, near Sulli- 
van (p. 113), measuring from 1(3 to 18 inches in width, has a quarter- 
inch border of light-green epidote, derived from the alteration of its 
glassy rim. These glassy borders are due to the rapid cooling of the 
material at its contact with the cold granite. A vertical diabase dike 
in Franklin (see p. 91) has darkened the shade of the granite and 
filled it with low-dipping close joints for a space of 10 feet on each 
side. Under the microscope the quartz particles and some of the 
feldspars show parallel cracks 0.25 to 1.25 mm. apart. A few typical 
thin sections of these dikes will be described in detail. 
The center of a 7-foot dike at the Mosquito Mountain quarry near 
Frankfort (p. 153) shows a network of minute lath-shaped crystals 
of lime-soda feldspar (labradorite) partly altered to a white mica, 
in the meshes of which i> a green hornblende: also some magnetite 
in fine particles and pyrite, with accessory titanite, apatite, and 
secondary epidote 
A 4-inch dike at the W. T. Ilavey (Whalesback) quarry, in North 
Sullivan (p. 118), shows a groundmass of fine hornblende and feld- 
spar (plagioclase), in incomplete crystals, with magnetite and thinly 
disseminated larger crystals of hornblende and lime-soda feldspar 
(labradorite), some large quartz particles, and a little pyrite. One 
feldspar crystal is almost completely altered to a white mica. 
A -J .j -foot dike at Campbell & Macomber quarry, on the west side 
of Somes Sound, on Mount Desert (p. 99), shows a groundmass 
of fine hornblende and feldspar (plagioclase) in incomplete crystals, 
with magnetite (?), pyrite partly altered to limonite, and lime-soda 
feldspar (labradorite). Some of the particles of the latter measure 
up to one-tenth inch in length by one-fiftieth inch in width and are 
largely altered to kaolin and a white mica. The hornblende in all of 
these dikes is regarded as a product of the alteration of augite. 
The geological age of these dikes has not been precisely determined. 
They are considerably more recent than the granite they traverse or 
the dikes of aplite and pegmatite which traverse the granite. In 
PL XI, J, one of these diabase dikes is shown crossing both a vein 
of pegmatite and a mass of diorite ("black granite"), at Round 
Pond, in Lincoln County. (See p. 139.) 
The diabase dikes are the result of an earth movement that either 
a Some of the dikes of that part of the coast havo boon described by V. Bascom : On 
some dikes in the vicinity of Johns Bay, Maine: Am. Geologist, vol. 23,«1897, pp. 275-280, 
Pis. IX, X, XI. 
