7S PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 17, 



from his own observations and those of others, respecting the mean 

 annual temperature at the limit of perpetual snow, in different lati- 

 tudes : — 



At Chimborazo, / Mean temperature") _qoo , qo '7_q/io ^ t.^ 



lat. = l°-28' S. I of the snow-line/ "'^^ + ^ '^—^^ ^ ^' 



At St. Gothard, \ _qoo fio.^_nno.o 



lat. =46°N. J » » -^^ ~ /-zo 6 



At the Polar Circle „ „ =32°-10°'8=21°-2 



Hence it follows that near the equator the snow-line is nearly 1000 

 feet lower than that of 32°, while at St. Gothard it is higher than 

 this latter line by about 2000 feet, and at some places on the polar 

 circle by about 3500 feet, according to Humboldt. But in that lati- 

 tude in the northern hemisphere the height of the snow-line above 

 that of 32° appears to be very variable, as might be expected from 

 the very different conditions under which different regions are si- 

 tuated along the same parallel of latitude. In north-eastern Asia 

 it is probably much greater than 3500 feet, while in Iceland the two 

 lines must nearly coincide. 



I am not aware of other similar observations on the temperature 

 of the snow-line, or on the relative heights of that line and of the line 

 of 32°. The height of the snow-line, however, has been ascertained 

 in several other places, and the height of the line of 32° F. may be 

 calculated, and their relative positions determined. Thus for the 

 Pyrenees (lat. =42° 30') we have by observation, — 



Height of snow-line = 9300 feet. 



The mean annual temperature at the level of the sea may be takeu 

 at 56°, and therefore the decrease up to the line of 32° will be 24° ; 

 and, allowing 320 feet ascent for a decrease of 1° F., we shall have, — 



Height of the line of 32° =7680 feet. 



Consequently the height of the snow-line will exceed that of the line 

 of freezing temperature by 1620 feet. 



A similar calculation for the Caucasus (lat. 42° 30'), where the 

 height of the snow-line is rather more than 10,000 feet, gives the 

 height of the line of 32° less than 8000 feet, and therefore lower 

 than the former by about 2500 feet. And again, for the Himalaya 

 we have similar results. On the south side of this range, in latitude 

 32° N., we may take the mean annual temperature, independently of 

 elevation, at 67° F., or 35° above the freezing temperature, and, 

 allowing 400 feet for a decrease of 1° F. in ascending the southern 

 slope of ^the mountains (art. 20, p. 77), the height of the line of 

 freezing temperature will be 14,000 feet. The height of the snow- 

 line, as given by Captain Strachey, is there 16,000 feet, or 2000 feet 

 higher than the former line. On the north side of the range, allow- 

 ing 2° F. in the mean annual temperature, independent of elevation, 

 for the difference of latitude as compared with the south side, and 

 480 feet of ascent for each degree of temperature (art. 20), we have 

 15,840 feet for the height of the line of 32°. Also we have, on the 



