44 
POPULAR SCIENCE REVIEW. 
snow escapes, a compact mass is formed, half snow and half 
ice, technically termed neve. By the force of gravity, the 
neve is slowly dragged downwards, moving partly by the 
upper layers slipping over the lower ones, and partly by 
the sliding of its whole mass bodily down the plateau. 
As warmer regions are entered, the neve gathers into the 
valleys, and becoming more and more consolidated, it passes 
by insensible degrees into the glacier. Still urged downwards 
the glacier continues to move by sliding and yielding, grind- 
ing down the rocks over which it passes, or grooving and 
scratching them in the direction of its motion. It is the long 
continuance of this action which has led many eminent men 
to believe that the glacier scoops out for itself the valley 
through which it moves; but though this view has been 
opposed, it certainly appears probable that, if it cannot 
originate, the glacier may enlarge and condition its bed. 
Whatever erosive power the glacier may possess, it is 
greatly assisted by that disintegration to which mountains are 
especially subject. Frost, storms, and avalanches are all 
active, so that as the glacier moves along, its borders become 
laden with the debris of falling rocks, giving rise to the so-called 
moraines , seen as longitudinal streaks on the glaciers shown 
in fig. 1. The edges of the glacier are in this way lined with 
ridges of stones, which to a large extent prevent the sun 
melting the ice beneath them. The consequence of this is 
that as the other portions of the glacier not thus screened 
melt away, the moraines relatively rise to a considerable 
height, until in some places, as at the upper portion of the 
Mer de Grlace near Mont Tacul, through the moraines the mar- 
ginal ice is elevated nearly fifty feet above the level of the 
surrounding glacier. Pushing far below the limits of per- 
petual snow, indeed correctly commencing only where the 
snow-line ends, the glacier reaches warm and cultivated 
regions, where its soiled substratum and weather-beaten 
surface are continuously melted, forming numerous turbid 
streams, which finally discharge themselves into the ocean. 
Measuring from their end or snout to their origin, the glaciers, 
of the Alps on an average are from ten to twenty miles long, 
and in the main about half a mile wide. Their depth has not 
been well ascertained, but in some places they have been 
bored 216 feet without reaching their bottom. Large as are 
these ice-streams, they are surpassed in other countries ; and 
even those are but pigmies compared to what must formerly 
have existed during a pre-historic age. 
The velocity with which the glacier moves along its bed 
has been the subject of careful study ever since the year 1841, 
when M. Agassiz, by exact and laborious observations, esta- 
