132 THE ICE AGE IN NORTH AMERICA. 



moving stream of ice, must be left in an unstratified condi- 

 tion — the coarse and the line being indiscriminately mingled 

 together. Now, this is the character of the extensive deposits 

 of loose material which cover what we designate as the gla- 

 ciated region. It is true that over this region there are exten- 

 sive stratified deposits. But these invariably mark the situa- 

 tion of abandoned lakes and water-courses. To these interest- 

 ing formations a special chapter will be devoted. But the 

 larger part of the region marked upon the map as glaciated 

 is covered with an unstratified deposit, in which are mingled 

 a variety of materials derived from rocks both of the locality 

 and of far-distant regions. Moreover, the pebbles in this de- 

 posit are the most of them polished and scratched after the 

 manner of those which we know to have been subjected to 

 glacial action. Ordinarily there can be no question of the 

 glacial character of this formation, even when no considera- 

 tions are taken into account except those which appear in the 

 deposit itself. Still, in certain situations, floating ice may 

 transport coarse material, and drop it in the midst of finer 

 silt, so as closely to simulate a true unstratified deposit. In 

 the majority of cases, however, the configuration of the coun- 

 try is such as to exclude the agency of floating ice from the 

 problem. 



We come, therefore, in the third place, to a mass of 

 recently discovered facts which would seem to place the 

 glacial theory above all question. When once the limit of 

 these unstratified deposits, containing striated stones and 

 transported material, had been accurately determined, it was 

 found that the margin was exceedingly irregular in two re- 

 spects. The southern edge of this deposit is both serrate 

 and crenate — that is, it does not follow a straight east-and- 

 west line, but in places withdraws to the north, and in others 

 extends in lobe-shaped projections far to the south. This 

 constitutes its serrate character. But it is the crenate char- 

 acter of its southern border which is of most significance. 

 The southern border, with its indentations and projections, 

 is not determined by any natural barrier. The southern 



