6 Mr. R. Mallet on the Temperature attainable 



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, and the pres- 

 sure being greatest where the pressing column comes into contact 

 with the fixed mass of rock, the extremity of the column sup- 

 posed homogeneous, or the parts adjacent thereto, are continu- 

 ally 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 the minimum of 217°. The crushed 

 fragments at this temperature are pushed aside by the advan- 

 cing column, whose extremity is thus surrounded by crushed 

 material at a temperature of 217°, 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 trans- 

 formed work of crushing of each successive cubic foot of rock 

 raises its temperature to a higher point, than that of the prece- 

 ding 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 surrounding it that have 

 already been heated by crushing ; so that, if T be the tempera- 

 ture produced in the first cubic foot crushed, and t be the tem- 

 perature of the crushed material which communicates a portion 

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

 successive cubic feet crushed may be illustrated by some such 

 series as the following : — 



Cubic feet crushed. 



No. I. No. II. No. III. 



T T+- T+ - + -... &c. 



n n m 



We have here supposed the column crushed at atmospheric 

 pressure ; but if crushed under an insistent column of 20 miles, 

 then the temperature T would be 4*28 times 217°=928°, and 

 the subsequent temperatures correspondingly increased. 



No limit arises to this continual augmentation of temperature 

 while the rock retains its rigidity ; after that has been seriously 

 impaired or lost, any further exaltation of temperature apart from 

 the detrusion or transport of fragmentary matter, as hereafter re- 

 ferred to, becomes dependent upon -the deformation and detrusion 

 of a more or less plastic mass. It is well ascertained, however, 

 by observation on a great scale, that granite remains rigid at a 



