260 R. Mallet—Temperature attainable by Rock-crushing. 
twenty statute miles, it will require rather more than 2°14, or, at 
twenty miles, 4:28 times as much pressure upon two opposite 
faces to crush it that it did when in air; and if we assume the 
displacement of the crushed particles after crushing to be the 
same as in the case of the cube crushed in air, then the 
work and the heat due to its transformation will be also 2°14, 
or 4-28 times as great. And, as in the case of the cube crushed 
in air the heat developed was sufficient to fuse at (at 2000° 
Fahr.) 0-108 of its own volume, or, in other words, the crush- 
ing of 10 eubic feet of the rock would be required to raise to 
that point one cubic foot, then in the case of the imaginary 
cube situated at the depth of ten miles enough heat would be 
evolved by the work of crushing each cubic foot to fuse 0-231 
cubic foot, or, at twenty miles, to fuse 0462 cubic foot of the 
same rock, or nearly half the volume crushed,—and this assum- 
to 20 miles depth. Therefore, under the pressure due to a 
depth of 20 miles and an initial temperature of 1000° Fabr., 
the heat developed by the work of crushing each cubic foot of 
rock will be sufficient to fuse its own volume. Thus also if we 
assume the fusing-point of the rocks not to be 2000° Fahr., as 
indicated by the author’s experiments on the cooling of slags, 
but considerably higher, say 2500° or more, we have still a 
sufficient supply of heat due to crushing alone to bring 08 0 
the entire volume to the fusing-point. 
These considerations, apart from all others yet to be adverted 
to, appear fully sufficient to refute the Rev. O. Fisher's first ob- 
jection above quoted; indeed the statement that if under any 
circumstances and in the rock-masses of nature ‘‘crushing can 
induce fusion, then the cubes experimented upon ought to have 
been fused in the crushing,” seems as unsupportable as_it 
would be to affirm that no heat is developed by the slow oxida- 
tion (eremacausis) into water and carbonic acid of a pound 0 
wood, which when burned develops a well-known amount of 
heat. 
The depths above assumed do not widely differ from those 
at which the foci of earthquakes have been found by the author 
(Report on Neapolitan Earthquake) in 1857, and by others 
since that time, and which may be presumed to indicate 1n 
some degree the possible depth of volcanic activity. 
he writer now proceeds to reply to the second objection of 
the Rev. O. Fisher as above quoted, which appears to him 
based entirely on a misconception of the physical conditions 
involved. Let us consider what will happen in the case of a 
prism or column of rock crushed against the face of an unyield- 
