QUATERNARY AGE. — GLACIAL PERIOD. 535 



(2.) The icebergs of the Atlantic bring their burdens from the Arctic mountains, hav- 

 ing gathered them while glaciers — for all icebergs are fragments broken from the lower 

 ends of glaciers; while the stones and earth of the Drift were often carried less than 

 fifty miles. Consequently, if icebergs were the means of transport in New England, 

 those icebergs must have commenced as glaciers about New England mountains, — an 

 idea which has its difficulty in the alleged fact (inferred from the scratches and stones) 

 that even Mount Washington was all submerged but five hundred feet, and Mount 

 Mansfield to its very top. 



(3.) Scratches made by icebergs that chanced to be grounded could not score so uni- 

 formly, and so completely, the whole surface of a country; and could not have been 

 made to conform so generally as they do, to the courses of the valleys. 



(4.) Bowlders hundreds of tons in weight were taken up from the low hills in the 

 Connecticut valley, and carried fifty miles, or less, to the south; and, if carried by ice- 

 bergs, the berg must have picked up the great mass by its foot, which is not possible. 



2. Glacier Theory. — This theory is sustained on the ground that — < 



(1.) Glaciers are known to transport bowlders, gravel, and earth; 

 and they may carry the material short distances as well as long. 



(2.) Glaciers make scratches in the rocks beneath them by means 

 of the stones they carry at bottom, precisely like those of the Drift 

 region as to regularity, kind, number, and all other peculiarities ; and 

 polished and rounded surfaces are other common effects from moving 

 glaciers. Moreover, the stones themselves are scratched or polished. 



(3.) Glaciers may make the scratches in large valleys in the direc- 

 tion of the valleys, when the main mass is moving in another direction. 

 For, while they take their general course from the grander slopes of 

 the upper surface of the ice-mass, the movement at the bottom will 

 accord, more or less perfectly, with the slopes of the land-surface ; 

 just as thick pitch, descending a sloping plane having oblique furrows 

 in its surface, would follow the general slope of the plane, but have 

 an under part diverted by the farrows. 



(4.) The presence of a considerable number of alpine or subalpine 

 plants, within the limits of the eastern United States (p. 532), can be 

 accounted for on the view of an era of glaciers, and not on that of 

 icebergs. 



(5.) The objection urged against the glacier theory, that the north- 

 ern part of the continents does not afford a slope southward, to favor 

 the movement, is of no weight, since no such slope was required. All 

 that was needed was a general southward slope in the upper surface 

 of the glacier ; or simply a greater accumulation of ice to the north 

 than to the south. The case is just like that of heaped-up pitch. If 

 stiff pitch be gradually dropped over a horizontal surface it will 

 spread, and continue so to do so long as the supply is kept up ; and, 

 if that surface rises at an angle in one direction, and there is no escape 

 in any other, it will first fill the space to the level of the edge, and 

 then drop over and continue onward its flow. So glaciers, if the 

 accumulation is adequate, may go across valleys and over elevated 



