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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.” And again,
in another place : “ Crystalline forces have rearranged whole
mountain-masses, producing a beautiful crystalline cleavage,
passing alike through all the strata.” 1 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.2 The
ooldness 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 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, ser. ii. vol. iii. p. 47 7.

9 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 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 one position, that
must of course determine a cleavage plane.”

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