514 E. MA.LLEI ON HIS THEORY OF VOLCANIC ENEROY. 



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, and 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 the two opposed prisms. It is these physical conditions 

 which "determine the localization " of crushing in the prism; and these 

 conditions have been disregarded in the Rev. 0. Fisher's objection. 



Having already shown that crushing alone under natural condi- 

 tions may suffice for fusion, and, secondly, that the heat produced 

 by crushing under natural conditions must be localized, the author 

 now proceeds to show that by successive crushing successive aug- 

 mentations of temperature must result. Let us consider the effects 

 of the successive crushing of a column or prismatic mass of rock 

 one extremity of which is continually urged against the face of 

 a fixed mass of rock which does not yield — a case which approxi- 

 mates to that which most frequently occurs in nature, and which, to 

 fix our ideas, we may suppose presents a face for crushing of one 

 square foot; and being continually urged forward, the compression 

 being greatest where the pressing column comes into contact with the 

 fixed mass of rock, the extremity of the column, supposed homo- 

 geneous, or the parts adjacent thereto, are continually crushed by a 

 succession of per saltum movements. .. 



The first cubic foot of the column that is crushed has its temperature 

 raised, let us suppose by 217° F. ; the crushed fragments at this tem- 

 perature are pushed aside by the advancing column, whose extremity 

 is thus surrounded by the crushed material at a temperature of 217° 

 plus the initial temperature, and the second foot in length of the 

 column becomes crushed ; but the material of this second cubic foot is 

 at a higher temperature before it is crushed than was the first cubic 

 foot, so that the heat due to the transformed work of crushing of 

 each successive cubic foot of rock raises its temperature to a higher 

 point than that of the preceding one, because each successive cubic 

 foot at the instant before crushing is at a temperature already 

 higher than the preceding ones, resulting from the heat taken up by 

 the uncrushed column from the hotter portions of material sur- 

 rounding it that has already been heated by crushing ; so that if 

 T be the temperature produced in the first cubic foot crushed, and t 

 be the temperature of the crushed material which communicates a 

 portion of its heat to the next cubic foot crushed, the temperatures 

 of the successive cubic feet crushed may be illustrated by some such 

 series as the following : — 



Cubic feet crushed. 

 No.l. No. 2. No. 3. 



T T+~" T+-+-. 



n n m 



