28 
THE GRANITES OF MAINE. 
shows the rift; and this is also quite marked in the hand specimen. 
It consists of exceedingly delicate fractures that meander across the 
quartz particles and some of the feldspars in a roughly parallel direc- 
tion. These cracks are filled with a highly refracting mineral (calcite 
or muscovite?), showing that the fractures are not recent. (See 
Herrmann" states that in Saxony the rift is parallel to the hori- 
ontal sheets or joints. That is true for short distances in the 
Maine quarries, but where the 
rift is horizontal and the sheets 
cm ve il crosses the sheets, and 
of course where the ri ft is ver- 
tical it crosses them through- 
out. Exceptionally, in one of 
th" quarries at Q.uincy, Mass., 
a foreman reported (<> the 
writer a deflection of the rift 
in apparent relation to the 
increasing inclination of the 
sheets. PI. Ill, .1, shows the 
relations of the rift to the 
sheet s at the Ryan-Parker 
quarry on Crotch Island. The 
structural diagrams a c c o m - 
panying the quarry descrip- 
tion- -how the relation of th- 
rift of grain, when vertical, to 
the various joint-. 
Rift and grain data were collected at 53 quarries of granite proper. 
At 29 of these the rift was vertical and at 24 it was horizontal and 
the grain was vertical. The courses of the rift and grain are dis- 
tributed as follows : 
Fig. 1.— Out linos of minerals in thin section (four- 
fiftieths inch square) of biotite-muscovite granite 
from Weskeag quarry, near Pleasanl Beach, 
South Thomaston, showing parallel rift cracks 
crossing quartz and feldspar particles marked 
gaud/). The finely shaded parts aremuscovite 
and bictite; the banded area, is oligoclase. The 
black pentagonal area is a crystal of garnet. 
Courses of rift. 
Number of quarries. 
6 
5 
'A 
9 
E.-W. to N. 85° E. mid N. 80° W 6 
X. 10° W.-N. 10° E 
N. 22°-50° W 
N. 30°-77° E 
N. 60°-70° W 
"Herrmann. ().. Steinhruchindustrie und Steinbruchgeologie, Berlin, 
L899, p. 109. 
