STRUCTURE OF MAINE GRANITES. 27 
a structure it is important to make sure that the grinding of the 
section has not in any way modified the original fractures. Tarr 
adds that at Cape Ann the rift does not traverse the b ' knots " or 
the basic dikes that cross the granite. 
Whittle gives two sketches made from polished surfaces of a well- 
known granite quarried by the Maine and New Hampshire Granite 
Company at Redstone, N. H. One of these sketches, made from a 
surface running at right angles to the rift, shows quartz and feldspar 
grains traversed by a generally parallel set of lines corresponding to 
the rift planes. The lines are more numerous in the feldspar than in 
the quartz grains. The other sketch, made from another specimen, 
shows besides the rift lines another less pronounced set intersecting 
these at right angles. This second set corresponds to the grain. 
Whittle calls attention to the fact that notwithstanding the marked 
rift and grain at this quarry the stone stood a co npression test of 
22,370 pounds to the square inch, and was, therefore, not appreciably 
weakened by the microscopic fractures. A visit made by the writer 
in 1906 to the quarry at Redstone, N. H., has corroborated Whittle's 
observations. The details of the rift and grain structure observed 
there will be discussed in a future publication. 
Another peculiarity of rift is that the angle of its inclination may 
at some places be modified by gravity. Thus in some localities a block 
will split at one angle from the top, but at another from the side ; or, 
again, at one angle where the mass of the block is at the right and at 
another where it is at the left of the line of fracture. Experienced 
granite workmen at Concord, N. H., and Quincy, Mass., report that 
at some places a block that would show a horizontal rift when split 
from one point of the compass (say the north) acquires an inclined 
rift if split from the south or the east or west. The cause of this 
is not apparent. There are also indications that a slight alteration 
of the feldspars may improve the rift. Finally, as is well known to 
granite quarrymen, rift and grain are modified by temperature, the 
effect of winter cold in New England (frost?) being to intensify the 
rift and grain where they are weak. 
A Norwegian geologist, Carl C. Riiber, in a work on the granite 
industry of Norway a describes an augite syenite with inferior rift and 
grain, in which the cleavage planes of the individual feldspar crystals 
are parallel to the two cleavage planes of the rock. No such relation- 
ship between rift and mineral cleavage has yet been made out in the 
Maine granites. 
Among the many thin sections prepared for this bulletin there is 
one from the medium-grained biotite-muscovite granite of C. E. Hud- 
son's Weskeag quarry, near Pleasant Beach, South Thomaston, which 
a Norges granit industri, Norges Geologiske undersogelse, Aarbog for 1893, No. 12, p. 45. 
