by Rock-crushing and its Consequences, 5 



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 0'8 of 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. 0. 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 oxidation {ere- 

 macausis) into water and carbonic acid of a pound of 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 in some 

 degree the possible depth of volcanic activity. 



The writer now proceeds to reply to the second objection of 

 the Rev. 0. 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 unyielding mass. 

 If the prismatic mass be not homogeneous throughout, crushing 

 will commence at the weakest place; if it be perfectly homoge- 

 neous, crushing will commence and continue where the prism is 

 in contact with a fixed mass, and that whether the prism be 

 crushed at one or both ends — because it is at such surface of 

 contact that the compression of the particles of the prism is 

 greatest, and where therefore the elastic limit of their cohesion 

 is first and successively overpassed. This may be seen illustrated 

 in the stonework of buildings the material of which is overloaded, 

 where crushing or spalling off of the ashlar stones only occurs 

 at and near the joints *. In either case, whether the prism 

 be homogeneous or not, the crushing must be localized either to 

 the end or ends of the prism, or to the plane of weakness where 

 it first yields, and which then becomes the crushing surfaces of 

 two opposed prisms. It is these physical conditions which 

 " determine the localization " of crushing in the prism, and 

 which conditions have been disregarded in the Rev. O. Fisher's 

 objection. Let us now consider the subsequent effects of the 



* See also E. Hodgkinson's experiments on the directions of fracture 

 of crushed materials, Brit. Assoc. Report, vol. vi. ; and Tredgold on Cast 

 Iron, by Hodgkinson, part 2, p. 319, and olate L 



