The Craven fault, for instance, extends for upward of thirty miles, and
along this line the vertical displacement of the strata varies from 600 to
3,000 feet. Professor Ramsay has published an account of a downthrow in
Anglesea of 2,300 feet; and he informs me that he fully believes that there
is one in Merionethshire of 12,000 feet; yet in these cases there is
nothing on the surface of the land to show such prodigious movements; the
pile of rocks on either side of the crack having been smoothly swept away.
On the other hand, in all parts of the world the piles of sedimentary
strata are of wonderful thickness. In the Cordillera, I estimated one mass
of conglomerate at ten thousand feet; and although conglomerates have
probably been accumulated at a quicker rate than finer sediments, yet from
being formed of worn and rounded pebbles, each of which bears the stamp of
time, they are good to show how slowly the mass must have been heaped
together. Professor Ramsay has given me the maximum thickness, from actual
measurement in most cases, of the successive formations in DIFFERENT parts
of Great Britain; and this is the result:
Feet
Palaeozoic strata (not including igneous beds)..57,154
Secondary strata................................13,190
Tertiary strata..................................2,240
--making altogether 72,584 feet; that is, very nearly thirteen and
three-quarters British miles.
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