6o 4 THE POPULAR SCIENCE MONTHLY. 



Thus it ran as a strait between the Bay of Biscay and the Mediterra- 

 nean, cutting off the Pyrenees and Spain from the rest of the continent. 

 It swept round the north of France, covering the rich fields of Tou- 

 raine and the wide flats of the Netherlands. It rolled far up the plains 

 of the Danube and stretched thence eastward across the south of Rus- 

 sia into Asia. 



By this time not a few of the species of shells which still people 

 the European seas had appeared. So long have they been natives of 

 our area that they have witnessed the rise of a great part of the con- 

 tinent. Some of the most stupendous changes which they have seen 

 have taken place in the basin of the Mediterranean, where, at a com- 

 paratively recent geological period, parts of the sea-floor have been 

 upheaved to a height of three thousand feet. It was then that the 

 breadth of the Italian Peninsula was increased by the belt of lower 

 hills that flanks the range of the Apennines. Then, too, Vesuvius and 

 Etna began their eruptions. Among these later geographical events 

 also we must place the gradual isolation of the Sea of Aral, the Caspian, 

 and the Black Sea from the rest of the ocean, which once spread from 

 the Arctic regions down the west of Asia, along the base of the Ural 

 Mountains into the southeast of Europe. 



The last scene in this long history is one of the most unexpected of 

 all. Europe, having nearly its present height and outlines, is swathed 

 deep in snow and ice. Scandinavia and Finland are one vast sheet of 

 ice, that creeps down from the watershed into the Atlantic on the one 

 side, and into the basin of the Baltic on'the other. All the high grounds 

 of Britain are similarly buried. The bed of the North Sea as well as 

 of the Baltic is in great measure choked with ice. The Alps, the 

 Pyrenees, the Carpathians, and the Caucasus send down vast glaciers 

 into the plains at their base. Northern plants find their way south 

 even to the Pyrenees, while the reindeer, musk-ox, lemming, and their 

 Arctic companions roam far and wide over France. 



As a result of the prolonged passage of solid masses of ice over 

 them, the rocks on the surface of the continent, when once more laid 

 bare to the sun, present a worn, flowing outline. They have been hol- 

 lowed into basins, ground smooth, and polished. Long mounds and 

 wide sheets of clay, gravel, and sand have been left over the low 

 grounds, and the hollows between them are filled with innumerable 

 tarns and lakes. Crowds of bowlders have been perched on the sides 

 of the hills and dropped over the plains. With the advent of a mild- 

 er temperature the Arctic vegetation has gradually disappeared from 

 the plains. Driven up step by step before the advancing flora from 

 more genial climates, it retired into the mountains and there to this 

 day continues to maintain itself. The present Alpine flora of the 

 Pyrenees, the Alps, Britain, and Scandinavia, is thus a living record of 

 the ice age. The reindeer and his friends have long since been forced 

 to return to their northern homes. 



