Page:Popular Science Monthly Volume 20.djvu/688

668 Now let us look at another picture of the past, but still within the human epoch. There was a time, then, when the European climate was so genial that many delicate southern species of plants nourished luxuriantly in regions where they can not now exist. Thus, in the neighborhood of Paris, the fig-tree, the Judas-tree, the laurel of the Canary Islands, and other southern species, found a congenial habitat. The Canary laurel does not grow farther north now than Toulon, on the borders of the Mediterranean. It flowers in winter, and repeated frosts would, therefore, prevent it reproducing its kind. That this plant formerly flourished near Paris is thus a striking proof of changed climatic conditions; we can not doubt that at one time the winters in Northern France must have been extremely genial. Moreover, we know, from the character of the plants with which the Canary laurel was associated in that region, that the climate must have been exempt from extremes—the summers were neither so dry nor so hot, and the winters were very much milder. The land and fresh-water shells which were contemporaneous with that remarkable flora in Northwestern Europe tell precisely the same tale, and this is still further illustrated and confirmed by the character of the mammalian fauna. Among the commoner animals at that time occupants of England, France, etc., were hippopotami, elephants, rhinoceroses, lions, tigers, hyenas, etc., and vast numbers of cervine and bovine animals which still occupy the temperate latitudes of Europe. That such genial climatic conditions were due in large measure to a great increase in the volume of warm water flowing into the North Atlantic seems just as certain as that the Arctic climate of the Glacial period was largely induced by a very considerable decrease, or even an entire stoppage, of that heat-bearing current. The presence of many Mediterranean shells in the ancient raised beaches of Scandinavia, the occurrence of mussel-banks in the coast-lands of Spitzbergen, the appearance here and there off the coast of Scotland, the Faröes, and Iceland, of southern species of shell-fish, and the presence of isolated colonies of southern mollusks in the Gulf of St. Lawrence, are all indicative of a former much greater influx of warm water into northern regions than is now the case. Those remarkable colonies of southern species are living evidence of the last epoch of extremely genial conditions experienced in Northwestern Europe—an epoch during which great forest growths overspread wide regions in the north—covering the British Islands, the Inner and Outer Hebrides, the Orkney and Shetland Islands, all Norway up to the extreme north, and most extensive areas which to-day lie submerged in the sea.

Thus, it will be seen how greatly the climate of Northwestern Europe has been, and may yet again be, modified by changes in the flow of the Gulf Stream. Now, if we glance at a map of America, it will be observed that only a narrow neck of land separates the Gulf of Mexico from the waters of the Pacific, and it is conceivable that,