Page:Popular Science Monthly Volume 76.djvu/482

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WE naturally look at things from the standpoint of the present, and regard the existing distribution of climates as the normal one. But even in our own times there are slight fluctuations of climatic conditions, for we hear wonderful stories from our elders of cold winters and hot summers, and tremendous storms of former years. The advances and retreats of existing glaciers give us surer testimony of recent fluctuations in temperature and moisture, as does also the shifting of the zones where wine grapes can be grown successfully in Europe.

If we go still further back into older history we find still stronger evidence of change, for in northern Africa and in central Asia there are remnants of ancient cities, evidently the flourishing capitals of prosperous peoples, where now is nothing but desert, and where even the most advanced modern skill in irrigation could not support the population of the old days.

And yet all the changes alluded to above may be only the secular variations in climate that we know are going on all the time. The climatic changes of the west coast which will be described in this paper are older than those fluctuations recorded in history, and much greater.

The old geological theory was that the earth cooled down slowly from the poles toward the equator, and that life first appeared at the poles. It was further thought that in the more remote geologic ages the interior heat of the earth was so great that there was little difference in temperature between the equator and the poles, and that, until Tertiary time, there was no differentiation into climatic zones. The Glacial epoch was supposed to be the culmination of this secular cooling off of the earth.

Then came the discovery of the old Tertiary fossil floras of Siberia, Alaska and Greenland, with abundant forests of trees that evidently lived in a temperate climate where it is now arctic. This was so remarkable that geologists had to invent some extraordinary explanation for the phenomenon. They rose to the occasion and invented the theory of the obliquity of the poles in early Tertiary time, to account, for the warm temperature under the arctic circle. This, however, did not agree with the known distribution of life at that time over the rest of the earth, and also the physicists declared this obliquity, or any obliquity, to be a mathematical impossibility.

Later it was discovered that there was a great glacial epoch in the