ithin the
polar circles. Many ingenious hypotheses have been proposed to account
for the warmer climate of earlier times, but are at best
unsatisfactory, and it appears to me that the true solution of the
problem may be found in the constitution of the early atmosphere, when
considered in the light of Dr. Tyndall's beautiful researches on
radiant heat. He has found that the presence of a few hundredths of
carbonic-acid gas in the atmosphere, while offering almost no obstacle
to the passage of the solar rays, would suffice to prevent almost
entirely the loss by radiation of obscure heat, so that the surface of
the land beneath such an atmosphere would become like a vast
orchard-house, in which the conditions of climate necessary to a
luxuriant vegetation would be extended even to the polar regions."

It is obvious that, in the production of complex effects of this kind,
various causes, whether astronomical or connected with the mutations
of the earth's crust, may have co-operated, and probably in all
extreme cases did co-operate.

In any case it is evident that the vicissitudes of climate and the
great pulsations of the crust, which have raised and depressed
portions of the surface and changed the position of its covering of
waters, have been potent agents in the hands of the Creator in
effecting the changes and succession of living beings, which are thus,
as Genesis intimates, children of the waters and of the land, and of
the influences of the heavens. It is also interesting in this
connection to observe that the occurrence of such periods of general
warm climate as that in the Miocene shows that it would have been
possible for man, under certain conditions, to have extended himself
far more widely in his Edenic state than we can conceive of in the
present condition of the earth. The modern world is perhaps even in
this way "cursed" for man's sake.

G.--DR. STERRY HUNT ON THE CHEMISTRY OF THE PRIMEVAL EARTH.

On looking back to the reference to this subject in Chapter V., I
think it may be desirable to present to the reader in some more
definite manner the conditions of a forming world; and I can not do
this in any other way so well as by quoting the words of Dr. Sterry
Hunt, as given in the abstract of his lecture on this subject
delivered before the Royal Institution of London in 1867:

"This hypothesis of the nature of the sun and of the luminous process
going on at its surface is the one lately put forward