Page:The New International Encyclopædia 1st ed. v. 01.djvu/470

ALPS. travel are so pleasant and easy. Railways and carriage roads traverse these mountains in all directions. At the best scenic points are excel- lent hotels, and guides are provided for conduct- ing visitors to all points. Hence every year tens of thousands of travelers visit the Alps from all parts of the civilized world.

As the Alps rise to heights of 12,- 000 to nearly 16,000 feet above the sea, in a re- gion of ample rainfall, the precipitation on these mountains is great, and gives rise to extensive glaciers, which originate near the summits and descend to different levels, the longest reaching within four or five thousand feet of sea level, and one of them, the Lower Grindelwald, having its termination at an elevation of only 3550 feet. The principal glaciers are found in the Bernese and Pennine Alps, and the group about Mont Blanc, although numerous smaller ones exist in many other parts of the system. The total number is estimated at 1200, of which 471 are in Switzerland and 462 in Austria, those in the former country being by far the largest, covering an area of 710 square miles; the total area of snow and ice in the Alps is about 1000 square miles. The largest and longest of the Swiss glaciers is the Aletsch, in the Bernese Alps, with a length of 16 miles (area, 50 square miles), and a breadth of ice of more than a mile. In length the Unteraar is next, with a length of 10.4 miles, followed by the Gorner in the Pennine Alps and the Viesch in the Bernese Alps, each of which is 9.4 miles in length. Other well- known glaciers are the Mer de Glace, above the Valley of Chamonix, Miage Glacier, which has its source on Mont Blanc, the Oberaar and the Unteraar, in the Bernese Alps, and the Rhone Glacier in the same group, near the Furka Pass.

Our present knowledge of glaciers, their origin, structure, flow, advance, recession, and the phe- nomena of erosion, has been mainly derived from a study of these Alpine glaciers. The present glacial system is but the last dying remnant of great ice sheets which once covered both flanks of the mountain system, descending to the plains and valleys on either side. As it shrank, it developed great rivers of ice, which carved mountain gorges and lake basins. The lake scenery of the Alps is unrivaled for beauty, grandeur, and diversity. The largest lakes in- clude Geneva, draining into the River Rhone, Neuchâtel, Bienne, Thun, Brienz, Lucerne, Zug, Zürich, Constance, Como, Lugano, Garda, and Maggiore. Tn the high mountains are cirques at the heads of all gorges not now occupied by ice, with little lakelets surrounded by frowning semi- circular sweeps of cliffs, hanging valleys, and smooth-sided, U-shaped gorges, planed and pol- ished, all bearing mute evidence of their glacial origin. Since the recession of the glaciers, the rivers in their turn have done a vast deal of erosion, but have not yet by any means effaced from the land the hand-writing of the ice. The main Alpine region is drained on the north by the upper system of the Rhine, includ- ing the Reuss, Aar, and Thur, and by south branches of the Danube, including the Iller, Lech, Isar, Inn, and Enns; on the east by west branches of the middle Danube, including the Drave and Save; on the south by the upper Adriatic coast streams, including the Taglia- mento. Piave, Brenta, and Adige, and by the northern branches of the Po, including the Mincio, Oglio, Adda, Ticino, Sesia, and Dora

Baltia; and on the west by the eastern tributaries of the lower Rhone, the Durance, Isère, and the upper Rhone itself.

The Alps are the result of intense folding and faulting of the strata, carried on for a long time, the folds and faults mainly trending northeast and southwest, accompanied and fol- lowed by long continued and intense erosion by ice and water. The net result of the earth move- ments was greatly to elevate the surface in a broad anticline, composed of many sharp anti- clines, synclines, and monoclines. Erosion has planed these off to a comparatively smooth curve, has removed the stratified beds in great part from the higher portions of the system, leaving only fragments of the older beds in limited lo- calities, and has laid bare vast areas of the un- derlying gneissic rocks. Hence the higher parts of the system are composed almost entirely of gneissic and allied rocks, while upon the flanks are found stratified beds, lying in various posi- tions with regard to the system, here lying up against it, there dipping away from it. The folding and faulting occurred in various geologic epochs, from Paleozoic times down, but was ap- parently most intense in relatively recent times, in the Mesozoic. They occurred at different times in different parts of the system, and not always or everywhere in the same direction, so that the result, in detail, is exceedingly compli- cated. The principal field of these movements, where the folding and faulting is most complica- ted and greatest, is north of the higher parts of the range, in other words, on the northern slope; here are found stratified beds succeeding each other in bewildering fashion. The southern or Italian slope is much simpler in structure.

The Alpine region is at the meeting place of the high middle-latitude marine climate of Western Europe, the continental climate of Central Europe, and the low-latitude marine climate of the Mediterranean regions. While it does not lie directly in the main path of the cyclonic disturbances which sweep across North- ern Europe from west to east, yet it does lie within the sphere of influence of these storm centres. Moreover, during the spring, numerous extended cyclones pass over the Alpine region; but they are less frequent in the winter and fall, and are almost totally lacking in the summer. This is the chief reason for the steady cold of the Alpine winter, with but few intensely cold waves, the serenity of its summer climate, and the harshness of its spring weather. The aver- age annual temperature on the northern Alpine boundary at altitudes of 1500 feet is about 48° F., while the seasonal averages range from about 30° F. in winter to 65° F. in summer. In winter temperatures usually descend as low as zero F., and in summer rise as high as 90° F. On the southern Alpine boundary, at altitudes of about 800 feet, the average temperature for the year is about 54° F., the variations ranging from 35° F. in winter to 72° F. in summer; but in winter the temperature usually does not de- scend below 15° F., and in summer may reach even 95° F. With increase of altitude above these regions there is on the average for the year a decrease in temperature of about 1° F. for each 330 feet of altitude; but the rate of decrease is much more rapid in summer than in winter. The average daily temperature is remarkably uniform in the Alps; but the temperature changes from day to night are excessive, on