Therefore, the slates to me are as a parable, on which I will not
enlarge, but will leave each reader to interpret it for himself. I
shall confine myself now to proofs that slate is hardened mud, and to
hints as to how it assumed its present form.
That slate may have been once mud, is made probable by the simple
fact that it can be turned into mud again. If you grind tip slate,
and then analyse it, you will find its mineral constituents to be
exactly those of a fine, rich, and tenacious clay. The slate
districts (at least in Snowdon) carry such a rich clay on them,
wherever it is not masked by the ruins of other rocks. At
Ilfracombe, in North Devon, the passage from slate below to clay
above, may be clearly seen. Wherever the top of the slate beds, and
the soil upon it, is laid bare, the black layers of slate may be seen
gradually melting--if I may use the word--under the influence of rain
and frost, into a rich tenacious clay, which is now not black, like
its parent slate, but red, from the oxidation of the iron which it
contains.
But, granting this, how did the first change take place?
It must be allowed, at starting, that time enough has elapsed, and
events enough have happened, since our supposed mud began first to
become slate, to allow of many and strange transformations.
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