e most
modern of those disturbed strata belong to the nummulitic formation,
which are regarded by the majority of geologists as Eocene or older
tertiary, an opinion not assented to by M. E. de Beaumont, and which I
cannot discuss here without being led into too long a digression.[248]

Perhaps a more striking illustration of the difficulties we encounter,
when we attempt to apply the theory under consideration even to the best
known European countries, is afforded by what is called "The System of
the Longmynds." This small chain, situated in Shropshire, is the third
of the typical systems to which M. E. de Beaumont compares other
mountain ranges corresponding in _strike_ and structure. The date
assigned to its upheaval is "after the unfossiliferous greywacke, or
Cambrian strata, and before the Silurian." But Sir R. I. Murchison had
shown in 1838, in his "Silurian System," and the British government
surveyors, since that time, in their sections (about 1845), that the
Longmynds and other chains of similar composition in North Wales are
_post-Silurian_. In all of them fossiliferous beds of the lower Silurian
formation, or Llandeilo flags are highly inclined, and often vertical.
In one limited region the Caradoc sandstone, a member of the lower
Silurian, rests unconformably on the denuded edges of the inferior (or
Llandeilo) member of the same group; whilst in some cases both of these
sets of strata are upturned. When, therefore, so grave an error is
detected in regard to the age of a typical chain, we are entitled to
inquire with surprise, by what means nine other _parallel_ chains in
France, Germany, and Sweden, assumed to be "ante-Silurian," have been
made to agree precisely in date with the Longmynds? If they are
correctly represented as having been all deposited before the deposition
of the Silurian strata, they cannot be contemporaneous with the
Longmynds, and they only prove how little reliance can be placed on
parallelism as a test of simultaneousness of upheaval. But in truth it
is impossible, for reasons already given, to demonstrate that each of
those nine chains coincide in date with one another, any more than with
the Longmynds.

The reader will see in the sequel (chap. 31[249]) that Mr. Hopkins has
inferred from astronomical calculations, that the solid crust of the
earth cannot be less than 800 or 1000 miles thick, and may be more. Even
if it be solid to the depth of 100 miles, such a thickness would be
inc