strata and the chalk._--We have evidence in England that
the strata of the ancient carboniferous group, already adverted to,
were, in many instances, fractured and contorted, and often thrown into
a vertical position, before the deposition of some even of the oldest
known secondary rocks, such as the new red sandstone.

Fragments of the older formations are sometimes included in the
conglomerates of the more modern; and some of these fragments still
retain their fossil shells and corals, so as to enable us to determine
the parent rocks from whence they were derived. There are other proofs
of the disturbance at successive epochs of different secondary rocks
before the deposition of others; and satisfactory evidence that, during
these reiterated convulsions, the geographical features of the northern
hemisphere were frequently modified, and that from time to time new
lands emerged from the deep. The vegetation, during some parts of the
period in question (from the lias to the chalk inclusive), when genera
allied to Cycas and Zamia were abundant, appears to have approached to
that of the larger islands of the equatorial zone; such, for example, as
we now find in the West Indian archipelago.[197] These islands appear to
have been drained by rivers of considerable size, which were inhabited
by crocodiles and gigantic oviparous reptiles, both herbivorous and
carnivorous, belonging for the most part to extinct genera. Of the
contemporary inhabitants of the land we have as yet acquired but scanty
information, but we know that there were flying reptiles, insects, and
small mammifers, allied to the marsupial tribes.

A freshwater deposit, called the Wealden, occurs in the upper part of
the secondary series of the south of England, which, by its extent and
fossils, attests the existence in that region of a large river draining
a continent or island of considerable dimensions. We know that this land
was clothed with wood, and inhabited by huge terrestrial reptiles and
birds. Its position so far to the north as the counties of Surrey and
Sussex, at a time when the mean temperature of the climate is supposed
to have been much hotter than at present, may at first sight appear
inconsistent with the theory before explained, that the heat was caused
by the gathering together of all the great masses of land in low
latitudes, while the northern regions were almost entirely sea. But it
must not be taken for granted that the geographical con