Page:Popular Science Monthly Volume 16.djvu/475

 indicating a very cold climate are found associated with those of a diametrically opposite character. Besides the mammoth, we encounter the ancient elephant, approaching that of India; the hippopotamus of African rivers peopled the waters of the Seine; while the hyena of the Cape frequented the meridian of France. The study of the forest flora, of which we find numerous remains in the contemporaneous tufa, leads to the same results; the vine, the laurel, the ivy, are found in abundance, not only in our southern regions, but also at Moret, near Paris. We find there also the much tenderer laurel of the Canaries. The northern trees of the same epoch were pines, lindens, maples, and oaks.

All these facts prove that the quaternary animals and plants characteristic of a cold climate existed only in the neighborhood of glaciers; and that, close by, in the valleys, lived creatures whose presence indicated a climate softer and more humid than ours. The mean annual heat necessary to their existence would be, at least, 14° or 15° centigrade. But, if we place ourselves now in the full Pliocene period, say near Lyons, we encounter the same vegetables, with others of a more southern character. At this epoch, in fact, the laurel-rose flourished on the banks of the Saone in company with the laurel, the avocatier of the Canaries, the bamboo, the magnolia, and the evergreen oak. The well-known climatic needs of these species warrant us in assigning to the country a mean annual temperature of 17° or 18° centigrade, and, as the actual mean temperature of Lyons is only 11°, we can judge of the difference of temperature which separates our epoch from that of the Pliocene. Moreover, as Saporta remarks, the figures which express the climate of Lyons during the Pliocene epoch are not only higher than those which apply to the neighborhood of Marseilles in Quaternary time, but, in place of corresponding to the 43° of latitude, these higher figures coincide with the 46°. They mark a progression of heat corresponding with latitude, the effect of which is to raise the temperature of northern regions in proportion as we bury ourselves in the past.

These curious phenomena appear still more evident and more general, if we transport ourselves in thought to the Miocene epoch. The entire unbroken documents abound in the boreal hemisphere, and we can there exactly determine the climates of all latitudes from 40° to 80°. Admirably preserved fossil plants, brought from the polar regions by different travelers, show that glaciers have not always desolated the pole. One of the principal deposits of these vegetables was found on the western side of Greenland at Atanekerdluk in 70° of latitude in the adjacent island of Noursoak. On the steep sides of a ravine one thousand feet deep, there exist entire beds of petrified leaves and other débris imbedded in a very ferruginous rock. The vast accumulation of leaves is truly surprising—trunks yet in place; flowers, fruit, insects accompanying them. M. Heer, who has studied