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applications of heat would have resulted, not entirely in raising 
the temperature as in checking and confining thermal effect to 
such molecular work as disintegration of the granite in certain 
directions along the lines of least resistance; and this effect is 
clearly seen on an examination of the burnt specimens—a 
blackened, ruinous, crumbling mass, varying in size from barely 
cohering to mere fine crumbly dust. The external surface of 
these columns was shelled off, and the facing to some depth 
ruptured and separated from the pillars, stripped away in the 
form of elongated ellipsoids, an inch to a few inches in thick- 
ness across the lesser axes, and thinning away to sharp irregular 
edges at the margin. The fiercest play of energy seemed to 
have been exercised on a portion around the middle third of the 
columns, leaving these once stately objects so many attenuated 
cores of concave outline. A distinction must not be omitted, 
in considering this work of destruction even in a rough esti- 
mation of it. The difference referred to is that between the 
effect wrought upon the three chief mineral constituents, Mica, 
Felspar and Quartz individually, and that left upon the granite 
mass itself. 
To determine the former purpose, recourse must be had to 
microscopic scrutiny; a consideration of the latter will follow. 
Thin sections of the granite were examined, but the burnt 
specimens could not be well ground thin, from their friable 
nature. Portions of these consisting of fine grains mingled 
with dust, had to be separated from the dust by means of a 
gauze sieve, in order to secure particles of requisite dimensions, 
namely, less than a millimetre, and these had to be mounted in 
Canada balsam on glass slips, so as to be fit for examination. 
The facts disclosed by these preparations were very simple. 
The disintegration of the felspars was quite complete. The 
Orthoclase crystals were minutely subdivided into very thin 
plates, through their several cleavage-planes, so as to show 
under polarized light the coloured bands and borders along the 
edges of each fragment, indicating the effect of stress and 
strain of the thermic vibrations which had acted so forcibly as 
to destroy the molecular symmetry of the crystallized mineral. 
R 
