W. Hopkins on Changes of Climate. 255 
than at present above the level of the sea. In such case it would 
be necessary to give to the Alpine region about the same addi- 
tional elevation as in the former case ($ 24) in order that the 
glaciers should descend to the lake of Geneva. 
_ 4he mean annual temperature of Snowdon would be nearly 
30° F., and the’ isothermal of the mean annual temperature of 
would pass through the mountains of the southwest of Ire- 
land Which present many indications of former glaciers. Along 
this isothermal, the line of 32° F. would coincide with the sur- 
face of the earth, and the height of the snow-line above it would 
be identical with the absolute height of that line, which would 
therefore be about 2500 feet, if the distance between these two 
lines should be the same as at present. For the reasons assigned, 
im the preceding paragraph, this distance, however, would un- 
doubtedly be much greater than at present. The oscillation 
fom Winter to summer temperature would amount to no less 
than 73° & F. (§ 15), whereas it is at present only 23°. The 
Present distance, therefore, between the two lines in question 
being taken at about 2500 feet, it is probable, I think, that in the 
“ase now considered, it would not be less than two or three times 
the knowledge we possess of the Altai mountains in the 
hortheast of Asia. ‘hose mountains rise to the height of 9000 
o 10,000 feet, and the mean annual temperature is under 32° F.; 
hing proof that the snow-line cannot in all probability be 
wer than the above estimate. : 
In Proceeding farther to the north, the snow-line would prob- 
ably Meet the level of the sea about the latitude of the northern 
Patt of Scotland. In all higher latitudes the surface of the earth 
_ covered with perpetual snow. 
was ollows, then, that if the Atlantic were converted into dry 
“4, it Would still be necessary, in order to obtain glaciers to the 
Buia: Tequired by observed phenomena, that the western part of 
aio, should be elevated into a range extending nearly from 
40th to the 60th parallel of latitude, and higher than the 
“ont Surface by some 4000 or 5000 feet. 
86. L now proceed to that which I consider by far the most 
the ortant of our hypothetical cases,—that in which we assume 
~ absenee of the Gulfstream and the submergence of a large 
portion of northern and central Europe beneath the ocean. There 
5° difficulty in this case in accounting for the existence of 
lati &rs in the northern parts of Scotland and in more northern 
~©8; but it is necessary to consider carefully how far the 
Whie ‘ons of their existence in the more southern latitudes in 
I will 2202 of glacial phenomena are observed, could be fulfilled. 
first consider the Snowdonian region. 
