102 
SCENERY OF SWITZERLAND. 
Rotifera (Philodina roseola) of a red or brownish 
colour. The firn is generally firm. When the tempera- 
ture is low, it becomes quite hard; except on hot 
days the foot sinks but little into it; usually it re- 
mains dry. The water which results from melting 
sinks into it, and freezes the snow below into a solid 
mass, which has a more or less stratified appearance, 
each yearly deposit forming a layer from one to three 
feet in thickness, which can sometimes be traced even 
to the lower end of the glacier. The firn attains in 
many places a great depth. Agassiz estimated that 
of the Aar glacier at 460 metres .* It moves slowly 
downwards, and when its upper end terminates 
against a rock wall, which of course retains its posi- 
tion, a deep gap is formed in spring, known as a 
Bergschrund, which widens during the summer and 
autumn, gradually fills up in winter, and reappears 
the next year. 
It is impossible to give any idea in words of the 
beauty of these high snowfields. The gently curving 
surfaces, which break with abrupt edges into dark 
abysses, or sink gently to soft depressions, or meet 
one another in ridges, the delicate shadows in the 
curved hollows, the lines of light on the crests, the 
suggestion of easy movement in the forms, with the 
* Systems Glaciaire . 
