THE ICE AGE AND ITS WORK. 783 



plateau of ice flowing outward by numerous glaciers into the sea. 

 The center of this plateau where Dr. Nansen crossed it was over 

 nine thousand feet above sea-level, and it may be very much 

 higher farther north. It, therefore, seems probable that the great 

 American ice-sheet was, at least, as high, and perhaps much 

 higher, and this would give sufficient slope for the flow to the 

 southern border. Of course, during the successive stages of the 

 glaciation there may have been numerous local centers from 

 which glaciers radiated, and during the passing away of the Ice 

 Age these local glaciers would have left striae and other indica- 

 tions of their presence. But so much of the area covered by the 

 drift all, in fact, south of the New England mountains and the 

 Great Lakes is undulating ground, hill, valley, and plateau of 

 moderate height, that here all the phenomena seem to be due 

 to the great confluent ice-sheet during the various phases of its 

 advance and its passing away. 



Sir Henry Howorth, in his very instructive work already 

 quoted, denies the existence and even the possibility of such ice- 

 sheets as those here indicated as having occurred in North Amer- 

 ica and Europe. He maintains that ice of the requisite thickness 

 could not exist, as it would be crushed or liquefied by its own 

 weight ; and further, that if it existed it could not possibly move 

 over hundreds of miles of generally level country, passing over 

 hills and valleys and carrying with it, either on its surface or in 

 its lower strata, the enormous quantity of bowlders, gravel, and 

 clay which we find everywhere overlying the present surface of 

 the ground. No doubt the difficulty does seem an enormous one, 

 but I think that it can be shown to be not so great as it seems ; 

 and it is certainly by no means so insuperable as that of the apoc- 

 ryphal floods, or " waves of translation " as they have been called, 

 to which he imputes the phenomena. He asks us to believe in one 

 or more gigantic waves sweeping over Eastern North America, 

 carrying bowlders to the summit of Mount Washington, nearly 

 six thousand feet high, scattering others over an area which is 

 roughly one thousand miles from east to west and six hundred 

 from north to south, and in its course producing those wonderful 

 strise, grooves, and furrows in the rocks photographed in the 

 American reports, and the enormous extent of smooth and 

 rounded rock surfaces that is found over this wide area. Besides 

 these there are two other phenomena absolutely inconsistent with 

 a diluvial agency. One is the enormous deposits of fine compact 

 clay bearing rounded and scratched stones thickly scattered 

 through it, utterly unlike any deposit produced by water, which 

 would necessarily leave the stones hundreds of miles behind the 

 place to which the fine mud would be carried. The other is the 

 existence of well-defined heaps, mounds, and ridges of gravel and 



