Why not? Some of the
richest red marl land I know, is, as I have said, actually being made
now, out of the black slates of Ilfracombe, wherever they are
weathered by rain and air. The chemical composition is the same.
The difference in colour between black slate and red marl is caused
simply by the oxidation of the iron in the slate.
And if my readers want a probable cause why the sandstones lie
undermost, and the red marl uppermost--can they not find one for
themselves? I do not say that it is the cause, but it is at least a
causa vera, one which would fully explain the fact, though it may be
explicable in other ways. Think, then, or shall I think for my
readers?
Then do they not see that when the Welsh mountains were ground down,
the Silurian strata, being uppermost, would be ground down first, and
would go to make the lower strata of the great New Red Sandstone
Lowland; and that being sandy, they would make the sandstones? But
wherever they were ground through, the Lower Cambrian slates would be
laid bare; and their remains, being washed away by the sea the last,
would be washed on to the top of the remains of the Silurians; and so
(as in most cases) the remains of the older rock, when redeposited by
water, would lie on the remains of the younger rock.
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