sea--a great authority, Neumayr, believes that it was
the greatest extension of the sea that is known in geology--and lowering
of the land would of itself tend to produce this condition, and it
may be that the very considerable volcanic activity, of which we find
evidence in the Permian and Triassic, had discharged great volumes of
carbon-dioxide into the atmosphere.

Whatever the causes were, the earth has returned to paradisiacal
conditions. The vast ice-fields have gone, the scanty and scrubby
vegetation is replaced by luscious forests of cycads, conifers, and
ferns, and warmth-loving animals penetrate to what are now the Arctic
and Antarctic regions. Greenland and Spitzbergen are fragments of a
continent that then bore a luxuriant growth of ferns and cycads, and
housed large reptiles that could not now live thousands of miles
south of it. England, and a large part of Europe, was a tranquil blue
coral-ocean, the fringes of its islands girt with reefs such as we
find now only three thousand miles further south, with vast shoals
of Ammonites, sometimes of gigantic size, preying upon its living
population or evading its monstrous sharks; while the sunlit lands were
covered with graceful, palmlike cycads and early yews and pines and
cypresses, and quaint forms of reptiles throve on the warm earth or in
the ample swamps, or rushed on outstretched wings through the purer air.

It was an evergreen world, a world, apparently, of perpetual summer.
No trace is found until the next period of an alternation of summer and
winter--no trees that shed their leaves annually, or show annual rings
of growth in the wood--and there is little trace of zones of climate as
yet. It is true that the sensitive Ammonites differ in the northern and
the southern latitudes, but, as Professor Chamberlin says, it is not
clear that the difference points to a diversity of climate. We may
conclude that the absence of corals higher than the north of England
implies a more temperate climate further north, but what Sir A. Geikie
calls (with slight exaggeration) "the almost tropical aspect" of
Greenland warns us to be cautious. The climate of the mid-Jurassic was
very much warmer and more uniform than the climate of the earth to-day.
It was an age of great vital expansion. And into this luxuriant world we
shall presently find a fresh period of elevation, disturbance, and cold
breaking with momentous evolutionary results. Meantime, we may take a
closer loo