known by the organic remains
contained in the formation. Though, perhaps, no leading geologist would
openly commit himself to an unqualified assertion of this theory, yet it
is tacitly assumed in current geological reasoning.

This theory, however, is scarcely more tenable than the other. It cannot
be concluded with any certainty, that formations in which similar
organic remains are found, were of contemporaneous origin; nor can it be
safely concluded that strata containing different organic remains are of
different ages. To most readers these will be startling propositions;
but they are fully admitted by the highest authorities. Sir Charles
Lyell confesses that the test of organic remains must be used "under
very much the same restrictions as the test of mineral composition." Sir
Henry de la Beche, who variously illustrates this truth, remarks on the
great incongruity there must be between the fossils of our carboniferous
rocks and those of the marine strata deposited at the same period. But
though, in the abstract, the danger of basing positive conclusions on
evidence derived from fossils, is recognized; yet, in the concrete, this
danger is generally disregarded. The established convictions respecting
the ages of strata, have been formed in spite of it; and by some
geologists it seems altogether ignored. Throughout his _Siluria_, Sir R.
Murchison habitually assumes that the same, or kindred, species, lived
in all parts of the Earth at the same time. In Russia, in Bohemia, in
the United States, in South America, strata are classed as belonging to
this or that part of the Silurian system, because of the similar fossils
contained in them--are concluded to be everywhere contemporaneous if
they enclose a proportion of identical or allied forms. In Russia the
relative position of a stratum is inferred from the fact that, along
with some Wenlock forms, it yields the _Pentamerus oblongus_. Certain
crustaceans called _Eurypteri_, being characteristic of the Upper Ludlow
rock, it is remarked that "large Eurypteri occur in a so-called black
grey-wacke slate in Westmoreland, in Oneida County, New York, which will
probably be found to be on the parallel of the Upper Ludlow rock:" in
which word "probably," we see both how dominant is this belief of
universal distribution of similar creatures at the same period, and how
apt this belief is to make its own proof, by raising the expectation
that the ages are identical when the forms are