sea, and the elevation of the land at given
places. When, in the course of the incessant
shiftings, it may happen that there is much
land, and high land about the equator, and
the bulk of water is at the two poles, then the
temperature of the whole earth would of
necessity be high. When it may happen that
the land prevails about the poles, and at the
equator there is chiefly water, then the
temperature would be low, and ice would hold
the world under its thumb far beyond the
limits of the Arctic and Antartic circles.
Variations of temperature, therefore, on the
surface of the earth, may, and most likely do,
depend upon the physical geography of the
earth's surface, not upon any special cause of
heat in the interior, or upon any strange
condition of surrounding air. The physical
geography of the world in past ages, as a whole,
cannot be ascertained. Let us suppose a
geologic Wyld, who should construct a model
of the earth, whereupon he arranged, with
elaborate care, each under each, the modelled
strata, twisted, where they are twisted, broken
where broken, continuous where continuous,
so that the earth's anatomy could be studied,
as one can study the anatomy of man upon a
papier maché model. From such a work it
would be easy to make out, so far as it goes,
contemporary sea and land through all past
ages ; but what shall tell us where was sea,
and where was land, over almost three-fourths
of the whole surface, over the part now
overflowed by water ? The arrangement of strata
and the fossils of the submarine earth are a
blank, except to our reason and imagination ;
of the existing dry land we have scratched
only here and there upon the surface ; and if
we knew all, it would be scanty knowledge.
It is impossible, therefore, to reconstruct the
seas and continents of former ages with enough
completeness for a demonstration of their
influence upon climate. Moreover, when we
are denied the power of examining so large a
part of the earth's crust, while we may reason
fairly upon what we find, and consider what
we see to be a fact, we have need to be very
cautious about denials based on what we have
not found : most unexpected things turn up ;
that fact is geological as well as social. We
came back to look for England, and here, not
far from the Cheapside of '51, a river, broad
and rapid, draining a large continent, flows
into a shallow sea. We sail up that river,
and we call ourselves at home ; though it be
not our island home, the site is English.
There is a monkey grinning at us. Well, we
have seen monkeys in Regent Street. But
there 's a sort of boa-constrictor. And look
through the trees, there is a tiger coming
down to the river-side to drink—bigger than
any Bengal tiger in the Regent's Park of
'51. Let us land upon our native soil.
There is an elephant, a very hairy fellow,
and the Mastodon too. There 's a great bison-
ox, the aurochs ; probably he lived long, and
made acquaintance with the ancient Britons.
Yonder stands gazing down upon us from the
hill a mighty elk, shedding yearly a pair of
antlers that weigh more than sixty pounds.
The span of his horns must be a dozen feet.
There is a bear ; and there goes a hysena snarling,
with an old bone in his mouth, which he is
taking to his kennel up in yonder cave. Any
dead meat is good to him, and a fine collection
of bones of contemporaneous animals, gnawed
and broken, he is laying up in his establishment
for the geologists of '51. There are
plenty of insects buzzing in the wood ; and,
look, there is a vulture, dipping down into
the dead flesh of an opossum. There 's
another serpent ; and here we disturb a family
of monkeys, who pelt down cocoa-nuts upon
us. There 's a wolf ; a fox ; let us go out
to sea again. There is a crocodile ; a turtle.
There 's a bird something like a pelican. There
is a strange fellow on the shore with a long
nose or a short proboscis, an odd compound
between horse, pig and elephant : what may
he be ?  O, he's the Palæotherium ! That
graceful fellow, the most graceful of the pig-
tribe (which in this age takes the place of
ruminants), looks not unlike the thing I never
nursed, a dear gazelle. 'Tis the Xiphodon.
Now we are at sea ; but wait awhile before
you begin fishing, though doubtless we may
catch odd-looking things ; they will be not
very much unlike perch, mackerel, or cod, or
herrings. You will find no salmon. I wonder
how the salmon comes by so much patronage
in '51 ; he's quite a novus homo. To be sure,
so is the best man, with the longest pedigree.
How far may we now be from Cheapside ?
Certainly some million of years. We have just
retreated through what geologists call their
tertiary period, and fallen back into the secondary.

Shall we have to fight our way through a
convulsion? No, never fear! The three great
periods are indeed separated by breaks in the
chain of the geologist: they are not, however,
breaks in nature, but in human knowledge.
We have seen volcanoes on our voyage back
into the past, and there is a volcano now; but
the vast effects produced by force on the
world's crust are not often produced in an
instant by a grand catastrophe; they are the
results of constant force applied through
enormous periods of time. During the break
between the secondary and tertiary periods,
there takes place a change in the whole series
of animals existing on the earth.

Here are sponges, and you may find
the water clouded with minute animalcules.
These little microscopic fellows, whose dried
skeletons are carried by the wind like dust
sometimes, and fall on our ship's rigging—
these little fellows increase and
multiply, very literally to replenish the earth.
What would Mr. Malthus have preached to
the father who produces eight hundred million
of children, grandchildren, and so on, in a
single month? Their skeletons, when they
are dead, bestrew the bed of the ocean in
some places, in a layer of immense depth, part