218 
ELEMENTARY GEOLOGY 
above, some of these large bergs must measure nearly 
a mile from the top to the submerged bottom. They 
carry with them a portion of the rock fragments of 
the glacier, and as they melt, these are strewn over 
the bed of the sea, sometimes at a great distance 
from their source. 
It is occasionally said that berg deposits have built 
shoals in the sea; but undoubtedly the action of ice- 
bergs in this respect has been greatly exaggerated. 
They are probably of much more importance in modify- 
ing climate than in making deposits in the ocean. 
WORK OF GLACIERS. 
CAUSE. 
Formed where snowfall exceeds melting; hence 
in higher latitudes even near sea-level, and among 
lofty mountains of lower latitudes, at higher eleva- 
tions. 
KIND. 
The valley glaciers: formed in higher land; de- 
scending in valleys. 
The Continental glaciers: of wide extent, sub- 
merging the land. Have valley glaciers at terminus. 
The Piedmont glaciers: nearly stagnant ice sheets 
on a plain, supplied by valley glaciers of mountain. 
CHARACTER- 
ISTICS. 
A snow field as the supply area. This compacts 
into ice and then slowly flows away, either reaching 
the sea and floating away in the form of icebergs, or 
melting. Has moraines, lateral, medial, terminal, 
and ground. If on the land has a stream at its end. 
Surface roughened by cracks caused by movement 
and by irregular melting. 
