"There have been fifteen climatic changes since the beginning of the glacial age, each change lasting 10,500 years, and each change reversing the season in the two hemispheres, the pole which had enjoyed continuous summer being doomed to undergo perpetual winter for 10,500 years, and then passing to its former state for an equal term. The physical changes upon the earth's surface during the past 80,000 years modified the changes of climate even in the Arctic regions, so that the intense cold of the former epochs was much modified during the latter epochs." Reckoning these climatic changes in their order, we had entered the epoch of a more genial temperature about fifteen hundred years ago; and if no disturbing change takes place during the present epoch, we may reasonably expect a gradual modification of our winters for nine thousand years to come. The changes to intense cold from perpetual summer during the greater part of the glacial period are supposed to have been caused by the high temperature of the north pole as compared to that of the south pole, owing to the distribution of land around the two, the south having almost none. Dr. Croll thinks it was caused by the varying inclination of the earth's axis, which produced the relative position of the two poles toward the sun to be periodically reversed at distant periods. Dr. James Geikie agrees with Croll on the reverse of seasons every 10,500 years during certain periods of high ellipticity of the earth's orbit. But it may be asked, "How could the fauna and flora propagate themselves under such conditions?" The flora itself at the quaternary age was of extreme vigor. We know this from the little which is left us, but more especially from the presence of a large number of herbivorous animals--stags, horses, elephants, rhinoceros, etc.--which animated the plains and valleys of Europe and America at the same time. Evidently they could not have lived and propagated themselves without abundant vegetation for nourishment and development.