70 
THE GRANITES OF MAINE. 
drilled by pneumatic or steam drills along- a proposed line of fracture 
under three sets of conditions. The block to be loosened must be: (A) 
Bounded laterally by two free ends (consisting either of two artificial 
channels or two joints or headings or dikes, or else of one of these and 
one channel) and bounded the other way by one quarried face and the 
desired line of fracture; or (B) bounded laterally by one channel 
and the proposed line of fracture and the other way by a heading or 
joint and a free face; or (C) not bounded laterally by any free end 
and the other w T ay only by the working face. In this case after the 
fracture is made the two other sides of the block must be cut either 
by blasting or splitting. In all these cases the boundaries of the block 
are the upper and lower surfaces of the sheets, and the lines of frac- 
A 
A 
A 
F 
~> -> 
Rift or gram 
: f : 
■ — • — — • — — • — • 
| Rift or grain ! 
; f 
! Rift or grain 
B 
C 
X 
• F 
'< o r 
; Rift 
F 
Rift or grain 
f y 
Rift or grain 
» J 
H 
D 
F ; 
O o : 
> ■< *■ 
F 
-> 
C 
\ Grain ! 
Fid. .",. — Diagrams illustrating irethcds of using explosives in Maine granite quarries. 
F, face ; J joint, heading, or dike : C, channel ; H, " hard-way " or " cut-off." The round 
dots represent blast holes. In diagram X the diagonal crack shows effect of not chan- 
neling on right side. In method shown in diagram B explosives are not used along the 
rift, and in that of II (Ilallowell granite) little or no explosive is used along the grain. 
ture must follow either the rift or the grain. Where the grain is 
weak it requires double the number of blast holes to effect a fracture 
along it that it does along the rift. Where there is no vertical rift or 
grain it is impracticable to use method C\ and in such cases, even with 
two free ends, channeling is resorted to. 
Exceptionally still another method is in use, which requires only 
one lateral joint face and one working face (besides the sheet sur- 
faces), the line of fracture forming the third side. But this method 
is regarded as hazardous by the more experienced men, for the frac- 
ture is apt to leave its direction of parallelism to the working face 
and swerve off diagonally to meet it. Processes A, B, and C are illus- 
