In Switzerland, where the elevations are so much greater, the snow-line varies from 8000 to 8800 feet above the level of the sea.[16] On Mont Blanc it is stated to be 8500 feet. The height differs on the northern and southern faces of the chain within those portions of the Alps that run east and west, but 8500 feet may be taken as the average.
We may be surprised to find that congelation rests at the same, or nearly the same, level in the Alps of Switzerland, and on the Corsican mountains eight degrees further south. But difference of latitude is no determinate rule for calculating the level to which the line of perpetual snow descends. There are other influences to be taken into the account, such as the duration and intensity of summer heats, the comparative dryness of climate, the extent of the snow-clad surface in the system generally, and more especially the height and exposure of particular mountains.[17] Thus the snow-line on the southern slope of the Alps is in some cases as high as 9500 feet. It may be conceived that as the great extent of snow-clad surface on the high Fjelds of Norway so much depresses the level of the snow-line in that country, so the great superincumbent mass resting on the summits of the higher Alps has a similar effect, reducing the average snow-line in Switzerland to nearly that of the Corsican mountains. The wonder is that Monte Rotondo and Monte d'Oro,—rising from a chain surrounded by the Mediterranean, in insulated peaks of no very considerable height, without glaciers or snowy basins to reduce the temperature,—should, in a climate where the sun's heat is excessive for eight months of the year, have snow on their summits in the months of July and August. I have observed the _Pico di Teyde_ in Teneriffe with no snow upon it in the first days of November, though it is 3000 feet higher than Monte Rotondo, and only five degrees further south. Mount Ætna, also, nearly 11,000 feet high, in about the same latitude as the Peak of Teneriffe (37° N.), is free from perpetual snow; but that may arise from local causes.
_Pisan Church at Murato.—Chestnut Woods.—Gulf of San Fiorenzo.—Nelson's Exploit there.—He conducts the Siege of Bastia.—Ilex Woods.—Mountain Pastures.—The Corsican Shepherd._