2 3 o THE POPULAR SCIENCE MONTHLY. 



could not be set aside, some thought it the same with the flood of 

 Noah, and others believed it to represent the chaos supposed to have 

 pervaded space just before the advent of man. Then it was fashion- 

 able to believe in a submergence of the land by an ocean freighted 

 with enormous icebergs, floating southerly from the pole. After this 

 the battle raged fiercely between the advocates of icebergs and gla- 

 ciers, the odds resulting in favor of the glacialists. Agassiz, with his 

 polar-cap theory, advocated the view of a globe entirely encircled by 

 ice, thickest at the poles, but covering the tropics with sufficient thick- 

 ness to destroy the Tertiary life. Since these days of controversy, 

 geologists have been accumulating facts in all glaciated countries ; 

 extreme views are being modified by their holders ; and the time has 

 come for consistent, reasonable generalizations in respect to the origin 

 and extent of glacial phenomena. 



"Where the glacial markings have been most studiously investigated, 

 it appears that an ice-sheet invariably occupies a definite area ; that a 

 mer de glace accumulates in the higher central portions, from which 

 glaciers move outwardly in all directions, extending as far as the de- 

 scending ground will permit, or the oceanic currents can convey the 

 icebergs broken off from the frozen mass without melting ; and that 

 these ice-streams carry with them fragments of rock scoring the ledges 

 as they pass along, thus affording the means for determining the exact 

 dimensions of the glaciated areas, even after the climate has moderated 

 and melted the ice. In Europe, the familiar Alpine district is con- 

 stantly quoted as an illustration of the nature of a glaciated region, 

 with its center of dispersion. Small ice-tributaries now cover the 

 slopes of the Rhone Valley, where formerly the solid mass pressed 

 down from the Bernese Oberland and the region of Mont Blanc, over 

 Lake Geneva and the broad valley of Switzerland to the flanks of the 

 Jura, forming an ice surface fifty miles wide, one hundred and fifty 

 miles long, and two thousand feet deep. On the south, other streams 

 have conveyed morainic materials equally far into the valley of the 

 river Po. Hence we can assign to this area, with its center of disper- 

 sion, a definite number of square miles, linking together the actual 

 glaciers with the traces of their former greater extension. No one 

 will question the correctness of the generalizations enlarging the limits 

 of the Alpine glaciated area. 



We proceed next to consider the proper extent of the Scandinavian 

 district, which will furnish an example more nearly analogous to that 

 of Eastern America. Erdmann's map in Geikie's " Ice Age " repre- 

 sents striae pushing northerly into the Arctic Ocean from Finland ; 

 southeast toward the White Sea and the Gulf of Finland ; southerly 

 in the south part of Sweden, turning to southwesterly toward the Cat- 

 tegat ; west, southwest, and northwest in Norway. Croll, in his work 

 on "Climate and Time," supplements this map by di-awing lines to 

 indicate the direction taken by the ice after leaving Finland and 



