DAVIS: GLACIAL EROSION. 
275 
cut off, as m Fig. 1, are sometimes fully as strong as those which 
naturally stand on the opposite side of the valley. The spurs 
generally remain in sufficient strength to require the river to follow 
its preglacial serpentine course around them, but they are some¬ 
times so far destroyed as to allow the river to take a shorter course 
Eig. 1. The glaciated valley of the Rhue. 
through what was once the neck of a spur. 1 The short course is 
not for a moment to be confounded with the normal cut-offs through 
the narrowed necks of spurs, such as are so finely exhibited in the 
meandering valleys of the Meuse and the Moselle. The short 
courses are distinctly abnormal features, like the rugged knobs to 
which the once smooth-sloping spurs are now reduced. 
It was thus possible in the valley of the Rhue to make a definite 
restoration of preglacial form, and to measure the change produced 
by glaciation. The change was of moderate amount, but it was 
highly significant of glacial action, for it showed that while a slender, 
fast-flowing stream of water might contentedly follow a serpentine 
course at the bottom of a meandering valley, the clumsy, slow- 
moving stream of ice could not easily adajit itself to so tortuous a 
path. The more or less complete obliteration of the spurs was the 
result of the effort of the ice stream to prepare for itself a smooth- 
sided trough of slight curvature; and if the rocks had been weaker, 
or if the ice had been heavier, or if the glacial period of the Cantal 
had lasted longer, this effort might have been so successful as to 
have destroyed all traces of the spurs. Fortunately the change 
actually produced, only modified the spurs, but did not entirely 
1 The short-cuts are sometimes narrow gorges incised in the half-consumed spurs • and 
in such cases, the displacement of the Rhue from its former roundabout course is 
probably to be explained by constraint or obstruction by ice. 
