Any one who saw that noble peak leaping high into the air, dominating
all the country round, at least upon three sides, and was told that
its summit consisted of beds much newer, not much older, than the
slate-beds fifteen hundred feet down on its north-western flank--any
one, I say, would have the right at first sight, on hearing of
earthquake faults and upheavals, to say--The peak of Snowdon has been
upheaved to its present height above and out of the lower lands
around. But when he came to examine sections, he would find his
reasonable guess utterly wrong. Snowdon is no swelling up of the
earth's crust. The beds do not, as they would in that case, slope up
to it. They slope up from it, to the north-west in one direction,
and the south-south-west in the other; and Snowdon is a mere
insignificant boss, left hanging on one slope of what was once an
enormous trough, or valley, of strata far older than itself. By
restoring these strata, in the direction of the angles, in which they
crop out, and vanish at the surface, it is found that to the north-
west--the direction of the Menai Straits--they must once have risen
to a height of at least six or seven thousand feet; and more, by
restoring them, specially the ash-bed of Snowdon, towards the south-
east--which can be done by the guidance of certain patches of it left
on other hills--it is found that south of Ffestiniog, where the
Cambrian rocks rise again to the surface, the south side of the
trough must have sloped upwards to a height of from fifteen to twenty
thousand feet, whether at the bottom of the sea, or in the upper air,
we cannot tell.
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