GEOLOGY. 279 



myself witnessed in Sicily, in 1828, its; effect in dissolving, in the month 

 of November, tiie snows which then fevered the summit and higher parts 

 of Mount JEtna. 1 had been told tint 1 should be unable to ascend to 

 the top of the highest, cone till the following spring ; but in 36 hours the 

 hot breath of the sirocco stripped off from the mountain its white mantle 

 of snow, and I ascended without difficulty. 



It is we'll known that the number of days during which particular winds 

 prevail, from year to year, varies considerably. Between the year IS 12 

 and 1820 the Fo'hn was less felt in Switzerland than usual ; and what 

 was the consequence ? All the glacier-?, during those eight or nine years, 

 increased in hight, and crept down below their former limits in their 

 respective valleys. Many similar examples might be cited of the sensi- 

 tiveness of the ice to slight variations of temperature. Capt. Godwin 

 Austen has lately given us a description of the gigantic glaciers of the 

 western Himalaya in those valleys where the sources of the Indus rise, 

 between the latitudes 35 and 36 N. The highest peaks of the Kara- 

 korum range attain in that region an elevation of 28,000 feet above the 

 sea. The glaciers, says Capt. Austen, have been advancing within the 

 memory of the living inhabitants, so as greatly to encroach on the culti- 

 vated lands, and have so altered the climate of the adjoining valleys 

 immediately below, that only one crop a year can now be reaped from 

 fields which formerly yielded two crops. If such changes c in be experi- 

 enced in less than a century, without any perceptible modification in the 

 physical geography of that part of Asia, what mighty effects may we not 

 imagine the submergence of the Sahara to have produced in adding to 

 the size of the Alpine glaciers ? If between the years 1812 and 1820, a 

 mere diminution of the number of days during which the sirocco blew 

 could so much promote the growth and onward movement of the ice, 

 how much greater a change would result from the total cessation of the 

 same wind ! But tnis would give no idea of what must have happened in 

 the glacial period ; for we can not suppose the action of the south wind to 

 have been suspended : it was not in abeyance, but its character was en- 

 tirely different, and of an opposite nature, under the altered geographical 

 conditions above contemplated. First, instead of passing over a parched 

 and scorching desert, between the 20th and 35th parallels of latitude, it 

 would plentifully absorb moisture from a sea many hundreds of miles 

 wide. Next, in its course over the Mediterranean, it would take up still 

 more aqueous vaoor ; and when, after complete saturation, it struck the 

 Alps, it would be driven up into the higher and more rarefied regions of 

 the atmosphere. There the aerial current, as fast as it was cooled, would 

 discharge its aqueous burden in the form of snow, so that the same wind 

 which is now called ' the devourer of ice " would become its principal 

 feeder. 



If we thus embrace Escher's theory, as accounting in no small degree 

 for the vast size of the extinct glaciers of Switzerland and Northern Italy, 

 we are by no means debarred from accepting at the same time Char- 

 pentier's suggestion, that the Alps in the glacial period were 2,000 or 

 3,000 feet higher than they are now. Such a difference in altitude may 

 have been an auxiliary cause of the extreme cold, and seems the more 

 probable now that we have obtained unequivocal proofs of such great 

 oscillations of level in Wales within the period under consideration. We 

 may also avail ourselves of another source of refrigeration which may 



