i Pleistocene Geology of Moravia Quadrangle 349 
mulation of deposits corresponding to the points where the drift 
was localized in the ice. Only in limited areas, perhaps, is any 
ground moraine due to this combination of conditions. 
■ When the ice-melting and the ice-supply are about equal the 
resulting accumulation of debris is simply the piling up at the 
ends of the lines of ice movement of such quantities of drift as the 
i ice holds along these lines. The most typical illustration of 
debris thus assembled exists in the areas of thickened drift called 
terminal moraines, and along valley lobes and tongues which 
deposit drift known as lateral moraine and loops. Such bands 
represent the debris gathered by the ice along its paths of motion. 
Furthermore, the upturning of layers in the ice results in shift- 
ing laterally considerable debris that otherwise might reach a distal 
position in accordance with the conditions mentioned above. 
This phenomenon has been observed in Greenland in both the 
ice-cap and the dependencies.^ 
The other great factor in the distribution of drift is found in the 
relief of the region under consideration. This control works itself 
out in two ways; first, the local topography to a large extent estab- 
lishes the course of ice-front drainage; second, this local topo- 
graphy gives the ice-front its particular form. I will discuss 
these points in reverse order. 
The influence which topography has on the outline of the ice- 
front is a question that can be unraveled largely through mapping 
the drift. Certain theoretical considerations, however, are of 
aid, since a semi-plastic body naturally assumes forms consequent 
upon the outlines of the area over which it rests. The ice will 
feed out farther along the more deeply incised valleys, and will 
be hindered in its progress by the highest divides. It follows, 
then, that if a given region contains valleys longitudinal to the 
direction of the ice-feeding, these valleys will each be occupied by 
a tongue or lobe of ice. When the ice with this irregular front 
maintains a fixed position, the feeding and the melting being about 
equal, drift accumulates in lines along its borders. 
If, however, the area has slight relief, then the form of ice-front 
will reflect more nearly the lines of impulse of the ice-sheet. This 
principle would give us in a fairly level country a uniform ice- 
^ R. D. Salisbury: Jour, of GeoL, vol. iv (1896), p. 791. Chamberlin and Salis- 
bury: Geology, voL i (1904), pp. 282-83. 
