fectly known, are really teleostean. Assuming, however, that the whole
of them did appear, as Agassiz believes, at the commencement of the chalk
formation, the fact would certainly be highly remarkable; but I cannot see
that it would be an insuperable difficulty on my theory, unless it could
likewise be shown that the species of this group appeared suddenly and
simultaneously throughout the world at this same period. It is almost
superfluous to remark that hardly any fossil-fish are known from south of
the equator; and by running through Pictet's Palaeontology it will be seen
that very few species are known from several formations in Europe. Some few
families of fish now have a confined range; the teleostean fish might
formerly have had a similarly confined range, and after having been largely
developed in some one sea, might have spread widely. Nor have we any right
to suppose that the seas of the world have always been so freely open from
south to north as they are at present. Even at this day, if the Malay
Archipelago were converted into land, the tropical parts of the Indian
Ocean would form a large and perfectly enclosed basin, in which any great
group of marine animals might be multiplied; and here they would remain
confined, until some of the species became adapted to a cooler climate, and
were enabled to double the southern capes of Africa or Australia, and thus
reach other and distant seas.

From these and similar considerations, but chiefly from our ignorance of
the geology of other countries beyond the confines of Europe and the United
States; and from the revolution in our palaeontological ideas on many
points, which the discoveries of even the last dozen years have effected,
it seems to me to be about as rash in us to dogmatize on the succession of
organic {307} beings throughout the world, as it would be for a naturalist
to land for five minutes on some one barren point in Australia, and then to
discuss the number and range of its productions.

_On the sudden appearance of groups of Allied Species in the lowest known
fossiliferous strata._--There is another and allied difficulty, which is
much graver. I allude to the manner in which numbers of species of the same
group, suddenly appear in the lowest known fossiliferous rocks. Most of the
arguments which have convinced me that all the existing species of the same
group have descended from one progenitor, apply with nearly equal force to
the earliest know