300 EXTERNAL APPEARANCE OF GLACIERS 
medial moraine. It is formed by the junction 
of the glaciers of the Lauter-Aar, on the right- 
hand side of the wood-cut, and the Finster-Aar, 
on the left ; and the union of their inner lateral 
moraines, in the centre of the diagram, forms 
the stony wall down the centre of the larger 
glacier, called its medial moraine. This moraine 
at some points is not less than sixty feet high. 
We have here an effect similar to that of the 
glacier-tables and the sand-pyramids. The wall 
protects the ice beneath it, and prevents it from 
sinking at the same rate as the surrounding sur- 
face, while its heated surface increases the melt- 
ing of the adjacent surfaces of ice, thus forming 
longitudinal depressions along the medial mo- 
raines, in which the largest rivulets and the most 
conspicuous sand-pyramids, the deepest wells and 
the finest waterfalls, are usually met with. As 
the medial moraines rest upon that part of the 
glacier which moves fastest, they of course ad 
vance much more rapidly than the lateral mo- 
raines. 
The terminal moraines consist of all the debris 
\ 
brought down by the glacier to its lower extrem- 
ity. In consequence of the more rapid movement 
of the centre of the glacier, it always terminates 
in a semicircle at its lower end, where these 
materials collect, and the terminal moraines, of 
course, follow the outline of the glacier. The 
