GLACIERS 



207 



in layers. It is evident that the transporting agent in ques- 

 tion was neither the wind nor running water. The size of 

 much of the material would at once exclude the former, 

 while various considerations as effectually dispose of the 

 latter. The largest bowlders of the till, weighing many tons, 

 are far beyond the transporting power of common streams. 

 Streams tend to round the stones rolled along their channels, 



FIG. 218. The shaded area shows the part of Europe covered by the con- 

 tinental glacier at the time of its greatest extent. (James Geikie.) 



and are unable to develop flat faces. Stream-laid beds are 

 in layers. The surfaces of water-deposited beds are without 

 notable irregularities, such as often characterize the till. 



Figure 216 shows deposits being made beneath a Green- 

 land glacier that possess all the characteristics of those 

 shown in Figure 215. So far as observed, all the deposits 

 being made by existing glaciers show these same characteris- 

 tics. Since existing glaciers are developing exactly the 

 features belonging to the drift of the great American and 



