374 On the Physical Geography of the Alps. 
of steep precipices and summits, and of massive snow-beds and 
glaciers, the depression of the limit of springs is, comparatively, 
very considerable ;—5. The diminution of the temperature in 
proportion to the altitude does not take place in an equal arith- 
metical or geometrical. progression. In the valleys it progresses 
more slowly than at the declivities and summits; and ceteris 
paribus advances more rapidly at higher elevations ;—6. Almost 
the same temperature is found at the limits of the growth of trees 
in the different Alpine ranges, although the altitude of this limit 
may itself somewhat vary. We may take 3°5° C. as the mean 
temperature. Immediately above the limit of arboreal growth we 
remark the most sudden diminution of the ground-temperature, 
and the most marked differences between the various springs ;— 
7. The springs in valleys are, at equal heights, warmer than those 
on the declivities and summits, and this is strikingly perceptible 
in the higher regions. In like manner, owing to the greater radi- 
ation from isolated rock-masses, a remarkable depression of the 
Famer sme ty takes place in the limestone Alps on the free 
eclivities towards the north ;—8. The minimum temperature of 
the highest springs in the Alps appears to be 0:8° C. ;—9. The 
height of the mountain-ranges has considerable influence on the 
ground-temperature. We find at equal altitudes above the sea- 
level the warmer springs where the mean elevation is greater ; the 
isogeothermal lines are thereby subjected to curvatures analogous 
to those of the lines of elevation in the district. 'These curva- 
tures are shown in a diagram representing a section of the Alps. 
The numerical results of the numerous observations (given in a 
tabulated form at pp. 269-273), made with reference to the tem- 
perature of the Alpine springs and the isogeothermal conditions 
of these mountains, are expressed in the accompanying table (see 
next e). 
The Changes effected on the earth’s surface by Erosion and 
Weathering are considered by M. Adolph Schlagintweit, in the 
twelfth chapter (pp. 274-316). The hydrographical conditions 
of the Alps are first insisted upon. The mass and annual distri- 
bution of the Alpine waters is noticed, also the determinations © 
the quantity of water flowing from glaciers, illustrated by a table. 
The temperatures of the Alpine lakes, springs, brooks, and rivers, 
the rapidity of flowing water, with a table, and the powers of 
suspension and solution exercised by the waters of the Alps, also 
accompanied by tables, are copiously treated of. With regard to 
the quantity of matter suspended in water, there is considerable 
Variation in different seasons of the year, and the quantity 18 
always considerably increased by heavy rains and falls of snow. 
It is important to notice the great quantity of matter suspen 
by glacier-streams. This is occasioned by the water, produced 
by the thawing of the surface, having no definite channel at the 
