ALTITUDES OF SNOW-FIELDS AND GLACIERS. 137 
parallel to the plane of perpetual snow,—the intervals, as 
observed by him at Alten, being given by the following 
table of limiting heights of vegetation above the sea :— 
VEGETATION IN LATITUDE 70°, 
The Pine (Pinus sylvestris) ceases at 237 metres = 780 Eng. feet. 
The Birch (Betula alba) 80 
The Bilberry (Vaccinium 
” 482, =1 ” 
ys 620 ,, = 2030 % 
Myrtillus), 
The Mountain Willow 
(Salix mirsinites), “3 656 ,, = 2150 36 
The Dwarf Birch (Betula 
nana), ei 836 ,, = 2740 iy 
The Snow-line, » 1060 ,, = 3480 a 
From the growth of the birch he has estimated the level 
of the snow-line in the islands of Qualoe and Mageroe, 
though neither of these rise to the requisite limit. It is 
probable, however, that the direct sea-blast to which those 
bare rocks are exposed, must act chemically upon vegeta- 
tion in a way which would render the deduction of the 
snow-line considerably doubtful—which doubt is confirmed 
by the more recent determination of the snow-line on the 
island of Seiland, opposite to Qualoe. 
Von Buch estimates the interval between the limit of 
the birch and perpetual snow at about 1,870 English feet 
throughout Norway; Wahlenberg estimates it at 1,960 
English feet ; which probably represents best the results 
in higher latitudes. 
And as a guide to fill up the gaps of direct observation, 
he adds, some determination of tbe limit level of the 
common birch in Norway, taken chiefly from the Gea 
Norvegica, from Naumann’s Travels, and from the obser- 
vations of Wahlenberg and of Smith, the Norwegian 
botanist. These he has given in tabular form, represent- 
ing the estimated altitude of the snow-line in twelve 
different localities, ranging from 594° to 71° 2’, adding to 
the mean limit of the birch 900 feet, as the limit of the 
birch and perpetual snow, and in six of the cases the alti- 
tude of the observed snow-line, which shows a general 
accordance, and, in some cases, an approximate conformity, 
of the one with the other. 
