1851.] HOPKINS ON CHANGES OF CLIMATE. 83 



mountains of sufficient magnitude to descend down to their present 

 bases, in consequence of a general elevation of western Europe, it 

 would be necessary that that region should be raised into an elevated 

 range from the polar circle to the south of the Alps, rising in some 

 parts to the height of 10,000 or 12,000 feet. 



25. I shall now take the case in which the old and new continents 

 are supposed to be united by the conversion of the basin of the At- 

 lantic into land. We should have, according to the estimate above 

 given (art. 15, p. 70), the mean annual temperature of the Alps 

 about 44° '5 F., or 11° lower than at the present time. The position 

 of the line 32° F. would therefore be lowered by about 3500 feet, 

 but the distance of the snow-line above it would be much increased 

 by both the causes which appear chiefly to influence that distance. 

 The oscillation of temperature from January to July would be 61° F. 

 instead of 34° as at present, and the quantity of snow falling during 

 the year would doubtless be much diminished by the entire absence 

 of sea in the surrounding region. It would seem probable that the 

 position of the snow-line would be as much raised by these causes, as 

 it would be lowered by the diminution of temperature. Moreover, it 

 is probable, that the glaciers would not descend so far below the 

 snow-line as at present, on account of the diminution of their mass, 

 arising from the diminished quantity of snow. I conceive it probable, 

 therefore, that the Alpine glaciers would not descend, in the case now 

 contemplated, to points less elevated 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 additional elevation as in the former case (art. 

 24) in order that the glaciers should descend to the Lake of Geneva. 



The mean annual temperature of Snowdon would be nearly 30° F., 

 and the isothermal of the mean annual temperature of 32° would pass ' 

 through the mountains of the south-west of Ireland which present 

 many indications of former glaciers. Along this isothermal, the line 

 of 32° F. would coincide with the surface 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, however, in the preceding paragraph, this distance 

 would undoubtedly be much greater than at present. The oscillation 

 from winter to summer temperature would amount to no less than 

 73° 5' F. (art. 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 case now con- 

 sidered, it would not be less than two or three times that quantity. 

 And this conclusion appears to be in accordance with the knowledge 

 we possess of the Altai moimtains in the north-east of Asia. Those 

 mountains rise to the height of 9000 or 10,000 feet, and the mean 

 annual temperature is under 32° F. ; and yet, as I am assured by 

 that distinguished traveller M. de Tchihatcheff, there are no glaciers 

 upon them of any magnitude, a sufficient proof that the snow-line 

 cannot in all probability be lower than the above estimate. 



In proceeding further to the north, the snow-line would probably 



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