THE CONTINENTAL GLACIERS OF POLAR REGIONS 277 



of the ice is, therefore, restricted to a relatively short distance, the 

 passageway between the nunataks, and the conditions are thus 

 to be likened to the fall of water at a raceway due to the sudden 

 descent of its surface from the level of the reservoir to the level of 

 the stream in the outlet. As is well known, there is under these 

 conditions a prodigious scour upon the bottom which tends to dig 

 a pit just above and below the dam a scape colk and carry 

 the materials up to the surface below the pit. Such a tendency 

 was well illustrated by the behavior of the water at the opening 

 of the Neu Haufen dam below the city of Vienna (Fig. 305 a). In 



Scale 1 : 670 (I'-SW). 



FIG. 305. a, Map showing pit excavated by the current below the opening in a 

 dam. 6, Nunataks and surface moraines on the Greenland ice. Dalager's 

 Nunataks (after Suess). 



the case of ice, material from the bottom may by the upward cur- 

 rent be brought up to the surface of the glacier at the lower edge 

 of the colk and thus produce a type of local surface moraine of' 

 horseshoe form with its direction generally transverse to the direc- 

 tion of ice movement (Fig. 305 6). 



Any obstruction upon the pavement of the glacier apparently 

 exerts a larger or smaller tendency to elevate the bowlders and 

 pebbles and incorporate them within the ice. Rock debris thus 

 incorporated is described as englatial drift. In the case of Green- 

 land glaciers this material seems at the ice front to be largely re- 

 stricted to the lower 100 feet (plate 13 A). 



Near the front of the inland ice the increased slope of the upper 

 surface greatly increases the flow of the upper ice layers in com- 



