e gloomiest and darkest parts of the forests of warm and temperate
regions, even extending to nearly the 46th degree of south latitude in
New Zealand. In equatorial countries, says Humboldt, they abound chiefly
in the temperate, humid, and shady parts of _mountains_. As we know,
therefore, that elevation often compensates for the effect of latitude
in the geographical distribution of plants, we may easily understand
that a class of vegetables, which grows at a certain height in the
torrid zone, would flourish on the plains at greater distances from the
equator, if the temperature, moisture, and other necessary conditions,
were equally uniform throughout the year.

Nor must we forget that in all the examples above alluded to, we have
been speaking of _living_ species; but the coal-plants were of perfectly
distinct species, nay, few of them except the ferns and pines can be
referred to genera or even families of the existing vegetable kingdom.
Having a structure, therefore, and often a form which appears to the
botanist so anomalous, they may also have been endowed with a different
constitution, enabling them to bear a greater variation of circumstances
in regard to light. We find that particular species of plants and tree
ferns require at present different degrees of heat; and that some
species can thrive only in the immediate neighborhood of the equator,
others only a distance from it. In the same manner the _minimum of
light_, sufficient for the now existing species, cannot be taken as the
standard for all analogous tribes that may ever have flourished on the
globe.

But granting that the extreme northern point to which a flora like that
of the Carboniferous era could ever reach, may be somewhere between the
latitudes of 65 degrees and 70 degrees, we should still have to inquire
whether the vegetable remains might not have been drifted from thence,
by rivers and currents, to the parallel of Melville Island, or still
farther. In the northern hemisphere, at present, we see that the
materials for future beds of lignite and coal are becoming amassed in
high latitudes, far from the districts where the forests grew, and on
shores where scarcely a stunted shrub can now exist. The Mackenzie, and
other rivers of North America, carry pines with their roots attached for
many hundred miles towards the north, into the Arctic Sea, where they
are imbedded in deltas, and some of them drifted still farther by
currents towards the pole