30 THE GRANITES OF MAINE. 
SHEETS. 
The division of granite into "sheets" or " beds " by jointlike 
fractures which are variously curved or approach horizontally, be- 
ing generally parallel with the granite surface, attracted the atten- 
tion of geologists long ago. Although this is the most striking fea- 
ture in every granite quarry and largely makes the granite industry 
possible, there is a great diversity of opinion as to its cause. Whitney ° 
writes : 
The curves are arranged strictly with reference to (lie surface of the masses 
of rock, showing clearly that they must have been produced by the contraction 
of the material while cooling or solidifying, and also giving very stronglj the 
impression that, in many places, we see something of the original shape of the 
surface as it was when the granitic muss assumed its present position. 
Shaler, a few years later, 6 attributed the sheet structure to ex- 
pansion due to solar heat. 
C. H. Hitchcock' notices in New Hampshire granite "numerous 
joints, the planes of which correspond very nearly with the slope of 
the hill," but does not undertake to explain them. 
Vogt<* states that the sheets in granites of southeastern Norway 
measure from 6 inches to 6 feet in thickness and dip from 8 to 33° 
on the sides of the mountains, toward the valley-, hut that they are 
horizontal on top and approximately parallel to the surface. He 
shows that they are of preglacial origin, attributes diem t<> the same 
cause that is postulated by Whitney for those in California, and 
regards them as parallel to the original surface of the granite masses. 
Harris.' . referring to the English granite quarries, writes: "In 
every quarry we visited we found that the direction of the 'beds' 
approximately corresponded with the outline of the hill on which it 
was situated." He oilers no explanation of the phenomenon, however. 
J. J. Crawford f describe- the sheet structure at granite quarries in 
Madera and Tulare counties. California, as consisting of " concentric 
layers conforming in a general way to the contour of the hills," but 
suggests no cause for them. 
Herrmann,' 7 who made a special economic study of the granites of 
Saxony, writes: 
" Whitney, J. D., Geology of California, vol. 1, 1865, Geology, p. 372; also pp. 227, 
417, and tigs. 49-54. 
''Shaler, N. S., Notes on the concentric structure of granitic rocks: Proc. Boston Soc. 
Nat. Hist., vol. 12, 1869, pp. 289-293. 
c Geology of New Hampshire, vol. '2, 1877, pp. 511-512 and plate opposite \>. 158, 
showing sheet structure at the " Flume." 
d Vogt, J. H. L., Sheets of granite and syenite in thoir relation to the present surface: 
Geol. Foreningens i Stockholm, Fohandl., 1879, No. 56, vol. t. No. 1 I : also Nogle, Bemaerk- 
ninger om Granit : Christiania videnskabsselsk. Fohandl., L881, No. 9. 
e Harris, George F.. Granites and our granite industries, London, 1888. 
f Twelfth Rept. State Mineralogist of California. 1894, pp. .".S4-387 and :; plates. 
Herrmann, O., Technische Verwerthung der Lausitzer Granite: Zeitsch. fur prakt, 
Geologie, Nov., 1895, Heft 2, p. 435. . 
