388 I KACMKNTS OF SCIENCE. 



ing to a solid state, can explain such phenomena. They 

 appear to me only resolvable on the supposition that crystal 

 line or polar forces acted upon the whole mass simultane 

 ously in one direction and with adequate force.&quot; And again, 

 in another place : &quot; Crystalline forces have rearranged whole 

 mountain-masses, producing a beautiful crystalline cleavage, 

 passing alike through all the strata.&quot; ] 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. 3 The 

 boldness of the theory, indeed, has, in some cases, caused 

 speculation to run riot, and we have books published on the 

 action cf polar forces and geologic magnetism, which rather 

 astonish those who know something about the subject. Ac 

 cording 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, alu 

 mina, potash, soda, and mica, mixed mechanically together. 

 In the course of ages the mixture became consolidated, and 

 the theory before us assumes that a process of crystalliza 

 tion afterward rearranged the particles and developed in it 

 a single plane of cleavage. Though a bold, and I think in 

 admissible, stretch of analogies, this hypothesis has done 



1 Transactions of the Geological Society, scr. ii. vol. iii. p. 477. 



2 In a letter to Sir Charles Lyell, dated from the Cape of Good Hope 

 February 20, 1836, Sir John Herschel writes as follows : &quot; If rocks have 

 been so heated as to allow of a commencement of crystallization, that is 

 to say, if they have been heated to a point at which the particles can be 

 gin to move among themselves, or at least on their own axes, some gen 

 eral law must then determine the position 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 par 

 ticles of the same nature have a general tendency to cue position, that 

 must of course determine a cleavage plane.&quot; 



