Evans. — On Coritact Metmnorphism. 563 



to the coal-measures to account for the production of the 

 anthracitic shales and anthracitic seam by rise of tempera- 

 ture only, if such a limitation were necessary. Personally, 

 1 do not think there is' any necessity to demand a great 

 rise of temperature. A moderate rise of temperature, 

 combined with a considerable increase of pressure, would, 

 I believe, completely determine the required elimination 

 of volatile matter, especially as that elimination would 

 be aided by the fissures sure to be formed by increase of 

 pressure. 



Alteration of Brown Coal at some Distance from the 



Dyke. 



It has at times been urged that the action of the dykes 

 must be limited to a few feet or yards at the most, and that 

 the alteration of brown coals at a distance of some 50 yards 

 cannot therefore be attributed to such action. The researches 

 of Professor Spring,* of Liege, upon the effects of pressure, 

 apart from those of elevation of temperature, seem to answer 

 this objection. 



Amongst other interesting conclusions. Spring states that 

 the rubbing or sliding of the particles of solid bodies over one 

 another under intense pressure powerfully promotes chemical 

 action between them ; and that when the particles of solid 

 bodies have been brought into contact by intense pressure, the 

 chemical action between them goes on even tvhen the pressure is 

 removed. 



If, therefore, during the injection of a dyke into or past 

 coal-measures the coal-seams are subjected, as we may surely 

 suppose, to intense pressure, there is reason to believe that 

 the natural processes of oxidation would receive a great 

 acceleration, and that even after the pressure had been 

 equalised again those oxidizing processes would, at any rate 

 for a considerable period, continue at the rate induced by 

 pressure. 



It is, I believe, somewhat in this direction that we must 

 look for an explanation of the altered brown coals of the 

 Brockley. ^ 



Experimental. 



It should — at least, indirectly — prove of value if experi- 

 ments were carried out with the object of determining the 

 effect of (1) pressure, (2) elevation of temperature, on the 

 ordinary (so-called unaltered) brown coals of the district. 

 The question as to whether the anthracites had ever been 



Journ. Chem. Soc. (London), 1890, p. 404. 



