olar oceans, where the tepid waters
of equatorial currents would freely circulate. The general humidity of
the atmosphere would far exceed that of the present period, for
increased heat would promote evaporation in all parts of the globe. The
winds would be first heated in their passage over the tropical plains,
and would then gather moisture from the surface of the deep, till,
charged with vapor, they arrived at extreme northern and southern
regions, and there encountering a cooler atmosphere, discharged their
burden in warm rain. If, during the long night of a polar winter, the
snows should whiten the summits of some arctic islands, they would be
dissolved as rapidly by the returning sun, as are the snows of Etna by
the blasts of the sirocco.

We learn from those who have studied the geographical distribution of
plants, that in very low latitudes, at present, the vegetation of small
islands remote from continents has a peculiar character; the ferns and
allied families, in particular, bearing a great proportion to the total
number of other plants. Other circumstances being the same, the more
remote the isles are from the continents, the greater does this
proportion become. Thus, in the continent of India, and the tropical
parts of New Holland, the proportion of ferns to the phaenogamous plants
is only as one to twenty-six; whereas, in the South-Sea Islands, it is
as one to four, or even as one to three.[195]

We might expect, therefore, in the summer of the "great year," or cycle
of climate, that there would be a predominance of tree ferns and plants
allied to genera now called tropical, in the islands of the wide ocean,
while many forms now confined to arctic and temperate regions, or only
found near the equator on the summit of the loftiest mountains, would
almost disappear from the earth. Then might those genera of animals
return, of which the memorials are preserved in the ancient rocks of our
continents. The pterodactyle might flit again through the air, the huge
iguanodon reappear in the woods, and the ichthyosaurs swarm once more in
the sea. Coral reefs might be prolonged again beyond the arctic circle,
where the whale and the narwal now abound; and droves of turtles might
begin again to wander through regions now tenanted by the walrus and the
seal.

But not to indulge too far in these speculations, I may observe, in
conclusion, that however great, during the lapse of ages, may be the
vicissitudes of tempera