Page:The American Cyclopædia (1879) Volume VII.djvu/844

 828 GLACIER the N. side of the extinct volcano of Mt. Shasta in northern California. From the summit, 14,440 ft. above the sea, according to him, we look down on three considerable glaciers. One of these has a breadth of three or four miles, and sends branches four or five miles down the canons. Its thickness is estimated in places to be 1,800 ft. or more, and its surface presents great crevasses, some of them 2,000 ft. long, and 30 or 40 ft. wide. Mr. S. F. Emmons has also found glaciers on Mt. Rainier or Tachoma in "Washington territory, and Mr. Arnold Hague on Mt. Hood in Oregon ; while more recently Mr. John Muir has succeeded in finding small gla- ciers much further southward in the sierras near the Yosemite valley on Mts. Lyell, McClure, and Hoifmann. They have the structure and movement of true glaciers, but the largest is not more than a mile in length, and they vary in breadth from half a mile to a few feet. The phenomenon of glaciers reaching the sea and becoming icebergs was noticed by Darwin in the gulf of Pefias, Patagonia. In northern Europe, it has been observed in Norway, in lat. 67 ST., and in America on the W. coast of Greenland. Upon the Himalaya mountains the glaciers appear from the accounts of modern travellers to be exhibited in masses of stupen- dous height, as well as of vast extent. In the "Himalayan Journals " of Dr. Joseph Hooker, those of the eastern portion of the range, in the territories of Sikkim and Nepaul, are de- scribed in detail, and mention is made of one which presents a vertical height of 14,000 ft., the source of which is the great Kinchinjunga, whose summit reaches the elevation of 28,000 ft. above the sea. Other gigantic glaciers in the central Himalaya are described by Dr. Thomas Thomson ("Western Himalaya and Tibet "), and by Col. Madden and Capt. Richard Strachey, in the '/Asiatic Researches," vol. xiv. Iceland, Spitzbergen, the Caucasus, and the Altai have their glaciers, which have been de- scribed by travellers ; but no regions have af- forded such convenient opportunities for study- ing them in detail as the Alps of Switzerland, Savoy, Piedmont, and Tyrol. Here, in the heart of Europe, they are found covering in de- tached portions an aggregate area computed at 1,484 sq. m. Between Mont Blanc and the bor- ders of Tyrol 400 are reckoned, of which the greater number are between 10 and 20 m. long, and from 1 to 2J m. broad. Their vertical thickness in many places is rated at 600 ft. ; their range is from above the snow line, which is from 7,500 to 8,000 ft. above the sea, down to the level of 3,500 to 3,000 ft. Lateral ravines have their glaciers, which join as branches the ice currents of the great valleys. This inter- esting region was studied by De Saussure in the latter portion of the last century, and his views were published in his Voyages dans les Alpes (1796). Charpentier is distinguished among later explorers as the able advocate of the theory explaining the motion of the gla- ciers, afterward sustained by Agassiz in his Etudes sur les glaciers (1840); and Prof. James D. Forbes of Edinburgh published in 1843 hia "Travels in the Alps," &c., with observations on the phenomena of glaciers made in visits to them repeated in ten different summers, in which he crossed the principal chain 27 times by 23 different passes. Many other distinguish- ed naturalists have aided not only to develop the true nature of glaciers, but to apply their phenomena to the explanation of past changes upon the earth's surface. Spread over the broad valleys, glaciers appear immovable. The snow disappears from their face in summer, and thousands of streams are then produced, which waste their material ; but with the re- turn of winter the covering of snow is renewed, and no change may be perceived in the great mass except such as can be referred to these superficial causes. But by comparative obser- vations made at different times, it is perceived that the great mass itself moves. The con- stant renewal of the waste at the lower ex- tremity, already referred to, is one evidence of this. Objects on the surface, too, are found to be continually moving down, even when their position on the ice itself is not changed. From the high precipices at the sides masses of rock and stone fall along the edges of the glacier, but it is obvious that they do not remain there in an immovable talus ; for where one glacier opens into another the piles of stones next the fork do not terminate as they join at this point, but are continued in a long mound of the same varieties of stone far down the glacier ; and as other branches come in, each adds its new mound, till sometimes as many as six parallel ridges are thus produced. These may come in contact below, and thus be reduced in num- ber, and even be blended with the piles at the edges. In some form, however, the mounds continue to the foot of the glacier ; and there ridges of bowlder-shaped stones and gravel are seen, which lie in front of the glacier, and are sometimes repeated in nearly parallel lines like the little ridges of sand and drift material along a sea beach, each one of which marks the limit of some previous high tide. So these great ridges of sand and stones, called moraines or borders, mark the limits reached by the foot of the glacier at former times ; and as the tide marks are all removed when a high-course tide again sweeps far up the breach, so the ridges at certain periods are observed to move on be- fore the advancing glacier, and mix together in a new and larger moraine at a greater dis- tance from the mountains. It is in these pe- riods that the habitable valleys of Switzerland are sometimes invaded by the terrible ice wall. Imperceptibly but irresistibly it is found ad- vancing upon the farms and cottages. The warm summer weather is obviously hastening its dissolution, yet its dimensions do not sensibly diminish. The green forests slowly disappear before it ; and the growing wheat almost feels its icy touch, before the soil is lifted by its i ruthless ploughshare. When, after such an