668 THE POPULAR SCIENCE MONTHLY. 



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 North- 

 western 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 cli- 

 matic 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 Faroes, and Iceland, of south- 

 ern 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 expe- 

 rienced in Northwestei'n 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, 



