moist and warm until the end of the Carboniferous period.
Once more I do not wish to enfeeble the general soundness of this
account of the evolution of life by relying on any controverted theory,
and we shall find it possible to avoid taking sides.

I have not referred to the climate of the earth in earlier ages, except
to mention that there are traces of a local "ice-age" about the middle
of the Archaean and the beginning of the Cambrian. As these are many
millions of years removed from each other and from the Carboniferous,
it is possible that they represent earlier periods more or less
corresponding to the Permian. But the early chronicle is so compressed
and so imperfectly studied as yet that it is premature to discuss the
point. It is, moreover, unnecessary because we know of no life on land
in those remote periods, and it is only in connection with life on land
that we are interested in changes of climate here. In other words, as
far as the present study is concerned, we need only regard the climate
of the Devonian and Carboniferous periods. As to this there is no
dispute; nor, in fact, about the climate from the Cambrian to the
Permian.

As the new school is most brilliantly represented by Professor
Chamberlin, [*] it will be enough to quote him. He says of the Cambrian
that, apart from the glacial indications in its early part, "the
testimony of the fossils, wherever gathered, implies nearly uniform
climatic conditions... throughout all the earth wherever records of the
Cambrian period are preserved" (ii, 273). Of the Ordovician he says:
"All that is known of the life of this era would seem to indicate that
the climate was much more uniform than now throughout the areas where
the strata of the period are known" (ii, 342). In the Silurian we have
"much to suggest uniformity of climate"--in fact, we have just the same
evidence for it--and in the Devonian, when land-plants abound and afford
better evidence, we find the same climatic equality of living things
in the most different latitudes. Finally, "most of the data at hand
indicate that the climate of the Lower Carboniferous was essentially
uniform, and on the whole both genial and moist" (ii, 518). The "data,"
we may recall, are in this case enormously abundant, and indicate the
climate of the earth from the Arctic regions to the Antarctic. Another
recent and critical geologist, Professor Walther ("Geschichte der
Erde und des Lebens," 1908), admits that the coa