t of all living existences; and to trace out the law of progress
from them to us.

It may not be unprofitable to bestow on these professions a somewhat
more critical examination than they have hitherto received, in order to
ascertain how far they rest on an irrefragable basis; or whether, after
all, it might not be well for paleontologists to learn a little more
carefully that scientific "ars artium," the art of saying "I don't
know." And to this end let us define somewhat more exactly the extent of
these pretensions of paleontology.

Every one is aware that Professor Bronn's 'Untersuchungen' and Professor
Pictet's 'Traite de Paleontologie' are works of standard authority,
familiarly consulted by every working paleontologist. It is desirable to
speak of these excellent books, and of their distinguished authors,
with the utmost respect, and in a tone as far as possible removed from
carping criticism; indeed, if they are specially cited in this place,
it is merely in justification of the assertion that the following
propositions, which may be found implicitly, or explicitly, in the works
in question, are regarded by the mass of paleontologists and geologists,
not only on the Continent but in this country, as expressing some of
the best-established results of paleontology. Thus:--Animals and plants
began their existence together, not long after the commencement of the
deposition of the sedimentary rocks; and then succeeded one another,
in such a manner, that totally distinct faunae and florae occupied the
whole surface of the earth, one after the other, and during distinct
epochs of time.

A geological formation is the sum of all the strata deposited over the
whole surface of the earth during one of these epochs: a geological
fauna or flora is the sum of all the species of animals or plants which
occupied the whole surface of the globe, during one of these epochs.

The population of the earth's surface was at first very similar in all
parts, and only from the middle of the Tertiary epoch onwards, began to
show a distinct distribution in zones.

The constitution of the original population, as well as the numerical
proportions of its members, indicates a warmer and, on the whole,
somewhat tropical climate, which remained tolerably equable throughout
the year. The subsequent distribution of living beings in zones is the
result of a gradual lowering of the general temperature, which first
began to be felt at the poles.