Other
beds may yet be found, but we saw that there was not a general
upheaval, as there had been in the Permian, and it is quite
possible that there were few or no ice-fields. We do not, in
fact, know the causes of the Permian icefields. We are thrown
upon the plant and animal remains, and seem to be in some danger
of inferring a cold climate from the organic remains, and then
explaining the new types of organisms by the cold climate. This,
of course, we shall not do. The difficulty is made greater by the
extreme disinclination of many recent geologists, and some recent
botanists who have too easily followed the geologists, to admit a
plain climatic interpretation of the facts. Let us first see what
the facts are.
In the latter part of the Jurassic we find three different zones
of Ammonites: one in the latitude of the Mediterranean, one in
the latitude of Central Europe, and one further north. Most
geologists conclude that these differences indicate zones of
climate (not hitherto indicated), but it cannot be proved, and we
may leave the matter open. At the same time the warm-loving
corals disappear from Europe, with occasional advances.
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