336 FHAGMlWTS Of 1 8C1ENCM. 



" that no retreat of the parts, no contraction of dimensions 

 in passing to a solid state, can explain s"uch phenomena. 

 They appear to me only resolvable on the supposition that 

 crystalline or polar forces acted upon the whole mass 

 simultaneously in one direction and with adequate force." 

 And again, in another place: " Crystalline forces have re- 

 arranged whole mountain masses, producing a beautiful 

 crystalline cleavage, passing alike through afl the strata."* 

 The utterance of such a man struck deep, as it ought to do, 

 into the minds of geologists, and at the present day there 

 are few who do not entertain this view, either in whole or 

 in part.f The boldness of the theory, indeed, has, in some 

 cases, caused speculation to run riot, and we have books 

 published on the action of polar forces and geologic 

 magnetism, which rather astonish those who know some- 

 thing about the subject. According to this theory whole 

 districts of North Wales and Cumberland, mountains 

 included, are neither more nor less than the parts of a 

 gigantic crystal. These masses of slate were originally fine 

 mud, composed of the broken and abraded particles of 

 older rocks. They contain silica, alumina, potash, soda, 

 and mica mixed mechanically together. In the course of 

 ages the mixture became consolidated, and the theory be- 

 fore ns assumes that a process of crystallization afterward 

 rearranged the particles and developed in it a single 

 plane of cleavage. Though a bold, and I think inadmis- 

 sible, stretch of analogies, this hypothesis has done good 

 service. Right or wrong, a thoughtfully uttered theory has 

 a dynamic power which operates against intellectual stag- 

 nation; and even by provoking opposition is eventually of 

 service to the cause of truth. It would, however, have 

 been remarkable if, among the ranks of geologists them- 



* Transactions of the Geological Society, ser. ii., vol. iii., p. 477. 



f In a letter to Sir Charles Lyell, dated from tlie Cape of Good 

 Hope, February 20, 1836, Sir John Herschel writes as follows: " If 

 rocks have been so heated as to allow of a commencement of crys- 

 tallization, that is to say, if they have been heated to a point at 

 which the particles can begin to move among themselves, or at least 

 on their own axes, some g-eneral law must then determine the posi- 

 tion in which these particles will rest on cooling. Probably that 

 position will have some relation to the direction in which the heat 

 escapes. Now when all or a majority of particles of the same nature 

 have a general tendency to one position, that must of course deter- 

 mine a cleavage plane." 



