ickness,
and extending for at least 300 miles from Vienna to Switzerland; and
although this great mass has been most carefully searched, no fossils,
except a few vegetable remains, have been found.

With respect to the terrestrial productions which lived during the
Secondary and Palaeozoic periods, it is superfluous to state that
our evidence is fragmentary in an extreme degree. For instance, until
recently not a land-shell was known belonging to either of these vast
periods, with the exception of one species discovered by Sir C. Lyell
and Dr. Dawson in the carboniferous strata of North America; but now
land-shells have been found in the lias. In regard to mammiferous
remains, a glance at the historical table published in Lyell's
Manual, will bring home the truth, how accidental and rare is their
preservation, far better than pages of detail. Nor is their rarity
surprising, when we remember how large a proportion of the bones of
tertiary mammals have been discovered either in caves or in lacustrine
deposits; and that not a cave or true lacustrine bed is known belonging
to the age of our secondary or palaeozoic formations.

But the imperfection in the geological record largely results from
another and more important cause than any of the foregoing; namely, from
the several formations being separated from each other by wide intervals
of time. This doctrine has been emphatically admitted by many geologists
and palaeontologists, who, like E. Forbes, entirely disbelieve in the
change of species. When we see the formations tabulated in written
works, or when we follow them in nature, it is difficult to avoid
believing that they are closely consecutive. But we know, for instance,
from Sir R. Murchison's great work on Russia, what wide gaps there are
in that country between the superimposed formations; so it is in
North America, and in many other parts of the world. The most skilful
geologist, if his attention had been confined exclusively to these large
territories, would never have suspected that during the periods which
were blank and barren in his own country, great piles of sediment,
charged with new and peculiar forms of life, had elsewhere been
accumulated. And if, in every separate territory, hardly any idea can be
formed of the length of time which has elapsed between the consecutive
formations, we may infer that this could nowhere be ascertained.
The frequent and great changes in the mineralogical composition
of con