the temperature appears to have been lowered. Nor was
the violent volcanic and diastrophic activity in the Mio-
cene associated with extreme climates. Indeed, there
appears to have been little contrast from zone to zone,
for figs, bread fruit trees, tree ferns, and other plants of
low latitudes grew in Greenland. Nevertheless, both at
the end of the Mesozoic and in the Miocene the climate
may possibly have been severe for a time, although the
record is lost. On the other hand, Kirk's recent discovery
of glacial till in Alaska between beds carrying an un-
doubted Middle Silurian fauna indicates glaciation at a
time when there was little movement of the crust so far
as yet appears. ¹ Thus we conclude that while climatic
changes and crustal movements usually occur together,
they may occur separately.

According to the solar-cyclonic hypothesis such a con-
dition is to be expected. If the sun were especially active
when the terrestrial conditions prohibited glaciation,
changes of climate would still occur, but they would be
milder than under other circumstances, and would leave
little record in the rocks. Or there might be glaciation in
high latitudes, such as that of southern Alaska in the
Middle Silurian, and none elsewhere. On the other hand,
when the sun was so inactive that no great storminess
occurred, the upheaval of continents and the building of
mountains might go on without the formation of ice
sheets, as apparently happened at the end of the Meso-
zoic. The lack of absolute coincidence between glaciation
and periods of widespread emergence of the lands is
evident even today, for there is no reason to suppose
that the lands are notably lower or less extensive now
than they were during the Pleistocene glaciation. In
fact, there is much evidence that many areas have risen

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