R. Malle-— Temperature attainable by Rock-crushing. 257 
upon the more rapidly contracting nucleus, it was not necessary 
to his argument to follow into detail the mechanism of local 
dislocation and crushing due to such descent. Nor would the 
limits of his paper admit of his entering into much detail as to 
the circumstances attending subterranean dislocation and crush- 
annual supply of heat transformed from the w of secular 
contraction were sufficient to meet the demands of existing 
voleanic action, that he should not overrate th rk s 
transformed ; and accordingly, in determining by experiment a 
measure for the amount of that work, the author view e 
work of crushing of unconfined or unsupported masses alone 
as the source of heat, this method being that only which could 
afford perfectly trustworthy experimental results. He paid no 
regard to the additional work that must attend the collision 
ho complete measure of the highest — that may 
through its means be locally developed ; 2n 
doubts which have been raised as to whether the temperature 
to which subterranean rocky masses can become raised by the 
heat evolved in their crushing and transportation of particles 
can be sufficient to bring more or less of these at such foci - 
of crushing and dislocation to the fusing-point of such mate- 
rials, which the author in his original paper assumes to be 
2000° Fabr, 
Professor Hilgard, occupying the chair of geology in the 
University of Michigan, U.S. in an able paper published in 
A 
M. Jour. Ser. Tarrp peed ‘cay X, No. 58.—Ocv.,, 1875. 
1 
