STRUCTURE OF MAINE GRANITES. 39 
Joints are exceptionally as curved " as the side of a ship." Thus 
at the White Granite Company's quarry, near Bluehill, there is a 
curved joint that covers a large segment of a circle and is continuous 
with two vertical joints, one of which strikes N. 50° W., and the 
other N. 52° E. This, as well as the sheet structure intersected by 
it, is shown in PL VI, B. 
Possibly related to such curved joints are what some New England 
quarrymen term " toe nails." These joints strike with the sheets, 
but extend only from one sheet surface to the next, and have a curve 
which sharply intersects that of the sheet structure. Such joints 
seem to be due to a strain different from that which produced the 
sheets. 
A tabulation of 179 observations of joint courses made by compass 
at 80 Maine quarries of granite proper yielded the following results : 
Courses of joints in granite as determined by 119 observations made at 80 
quarries in Maine. 
Direction. Number of observations. 
N. 12° W.-N. 15° E 19 
N. 20°-30° E 13 
N. 20°-30° W 8 
N. 32°-50° E 25 
N. 35°-50° W IS 
N. 55°-70° E___" 19 
N. 55°-70° W 27 
E.-W. to N. 75° E. and N. 75° W 50 
The joints of the dominant system extend approximately east to 
west; those of the systems next most common extend approximately 
northeast and northwest, east-northeast, and west-northwest, and 
north and south. 
The spacing of the joints varies considerably, ranging from 1 foot 
to 500 feet, but usually from 10 to 50 feet. 
In some localities the jointing is very irregular. Thus at the Ellis 
& Buswell (Ross) quarry, near Biddeford (fig. 39, p. 18'2),the granite 
is broken up into various polygons, which at the surface, where 
weathering has made inroads, resemble bowlders. Quarries opened 
in such places are called bowlder quarries. Another sort of irregu- 
larity in joints consists in their discontinuity or interim ttence, their 
strike and dip for the short spaces in which they occur being uniform. 
HEADINGS. 
In some places joints occur within intervals so short as to break 
up the rock into useless blocks. For a space of 5 to 50 feet the joints 
may be from 6 inches to 3 feet apart. A group of close joints is 
called by quarrymen a " heading," possibly because, when practicable, 
