THE BOUNDARY-LINE BETWEEN GEOLOGY AND HISTORY. 225 

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 up the valleys were it not for the milder temperature of the latter, wliicli 

 melts them and puts an end to their progress. Frequently rocks fall 

 down upou them from the precipices above and are carried down into 

 the valley. These stones collect at the lower end of the glaciers, form- 

 ing heaps called moraines, and are usually in the shape of a half-moon 

 with its concave side toward the glacier. If a long-continued cold 

 temperature sets in, which favors the progress of the glacier, the latter 

 will push before it the moraine, along with a mound of earth, uprooted 

 trees, &c. ; and if the temperature rises, the lower end of the glacier 

 melts away and the glacier apparently recedes, leaving the moraine at its 

 advanced position as a mark of its extent to future observers. 



Such advanced moraines are found with nearly all the larger groups 

 of glaciers in Central Europe, some of them miles away from the pres- 

 ent end of the glacier, as, for instance, at Eerne and Zurich in Switzer- 

 land. Mountain-ridges like the Carpathian, which have no ice near 

 them to-day, have ancient moraines. Marienzell rests upon bowlders 

 brought to their present position by glaciers. At the foot of the 

 Rosalia JMountains are found the traces of glaciers which formerly ex- 

 isted on the Wechsel and Schnee IMountains. 



Since these moraines extend directly across the valleys, they often ob- 

 struct the water-courses and give rise to Alpine lakes. The upper lake 

 of Gosau is bounded toward the valley by the moraine of the western 

 Dachstein glacier. The " Meerauge," a lake in the Tatra Mountains, is 

 hemmed in by a similar moraine, although at the present time there is 

 neither a glacier nor even an extensive snow-field in the place. All 

 these moraines are a proof that a much colder temperature must have 

 prevailed in these regions at a time after they possessed their present 

 formation, and if these traces of past glaciers are so numerous in the 

 latitude of Switzerland, we can easily imagine that they are still more 

 extensive farther north, in Scandinavia. 



The northern part of Europe also presents other striking phenomena, 

 which must be described in detail. The topography of a region depends 

 on the relative height of its different parts ; the distribution ot land 

 and water on the absolute height of the whole. The level of the sea 

 may be taken as unchanged. By the " continental" elevation and de- 

 pression of large regions, considerable changes have been produced in 

 the outlines of the dry lands, and these changes are divided into three 

 great epochs. 



1. The first epoch is that of depression. Then the sea extended as far 

 as Hanover, and from Breslau to Cracow. The whole I^ortli German 

 and Central Kussian lowlands were under water. Scandinavia and 

 parts of the British Isles were above the surface of the sea. In Scandi- 

 navia the ends of the glaciers reached down into the sea, just as they 

 do in arctic regions in the present day, and from time to time a large 

 piece, often covered with huge blocks of the moraine, would separate, 

 float down to the southward, and there deposit its load. Thus it hap- 

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