236 FRAGMENTS OF 8C1RNCB. 
" that no retreat of the parts, no contraction of dimensions 
in passing to a solid state, can explain such 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 us 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. Hi., p. 477. 
f In a letter to Sir Charles Lyell, dated from the 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 general 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." 
