QUATERNARY AGE. — GLACIAL PERIOD. 535 



shells. The greatest height of shore shell-beds in or near the United States is 470 feet; 

 and this occurs on the St. Lawrence (p. 550); nothing of the kind occurs over the Ohio 

 region, north or south of the river. 



(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 stones in the bottom of bergs that chanced to be grounded 

 could not score so uniformly, and so completely, the whole surface of a country. They 

 would make only distant deep channelings, unless the ice lay regularly over the whole 

 bottom, — a condition which may be that of the foot or under surface of a glacier, but 

 not that of an iceberg. 



(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. 



(5.) If the Continent were so submerged that the Mississippi valley and the St. Law- 

 rence were one continuous oceanic channel, the current in the Mississippi part would 

 be one from the south, as a continuation of the Gulf Stream, rather than one from the 

 north ; and this would be in direct disaccord with the facts with regard to the course of 

 Drift transportation over the region. 



(6.) The fact that there is commonly a conformity between the directions of scratches 

 in the larger valleys and the courses of these valleys, is incompatible with the idea 

 that icebergs did the work of abrasion; for, in a deep sea, they could not have found the 

 currents needed to carry them along so many and various courses. 



(7.) The submergence of the northern part of America, as far as the southern limits 

 of the Drift, would have made a warm climate for the continent, and not a glacial (p. 

 44); and, hence, there is great difficulty in accounting for either icebergs or glaciers, 

 upon this view. 



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 

 regions, 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 moviug 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 furrows. 



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

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



