266 BR. Malle—Temperature attainable by Rock-crushing. 
of the heat evolved would have been dissipated; and this, we 
shall see further on, must be the case in nature. When two 
rock-surfaces are urged against each other in the shell of our 
globe by the gradual withdrawal of support by contraction of 
the nucleus, the rocky masses for great distances from the op- 
posed surfaces are brought into a state of elastic compression, 
gradually increasing up to the crushing-point somewhere, when 
a greater or less portion of rock suddenly gives way by crush- 
or the 
feet per second, and that would be less than ;,;';; of the velocity 
with which the same would have been crushed if circumstance 
as in the shell of our globe. And if we extend our view from 
the crushing of a cubie foot or two to that of a cubic mile or 
more, we see that there would be very little of the total heat 
evolved lost by dissipation, there being scarcely any time in 
which that could occur, the possible rate of crushing of a cubic 
mile being less than half a second. 
In the case of a very large mass of rock crushed simultane- 
ously, or nearly so, as every portion of the rock evolves heat 
proportionate to the crushing-work done upon it, so the heated 
portions of crushed material situated near the exterior of the 
