3. Volcanic Mountains.— Mountain ranges are rarely formed by volcanic action alone, but isolated peaks are often of this origin. Vol canic cones, great piles of lava and ash, form one type, of which Mount Shasta is one of our best-known examples. Recently formed cones are often beautifully symmetrical, as are those of Hood and Shasta. But as soon as activity ceases, denudation sets in, the cone becomes gashed with valleys, and in course of time only the harder central plug is left as a volcanic neck. Such plugs are common in the Puy region of central France, and the Mount Taylor region of New Mexico. Sometimes masses of igneous rock are intruded under sedimentary beds in the form of laccoliths (q.v.), arching up the beds to form elevations such as the Henry Mountains in Utah. Many regions of folded mountains also have numerous volcanic peaks, as.in the case of Mount Hood and other cones on the folded Cascade Range. See BATHOLITH 5 ; CONE; LACCOLITH ; VOLCANO.
4. Residual Mountains.— When great areas are uplifted bodily without folding, they form plateaus. When such a plateau is greatly dis sected, it becomes mountainous in topography, merely because some parts are not worn away as fast as others. These are residual moun tains, or mountains of circumdenudation. The Allegheny plateau is a region of this type.
Whatever may be the cause which makes the uplift on the earth's surface, denudation be gins as soon as the peak appears, and formation and destruction are conjoint agents in making the mountains what they are on the surface of dig earth. Before the process of folding is completed the elements have begun their work of shaping and sculpturing, but the destructive agents at first work more slowly than the con structive. The chief agents of changes after formation are frost, wind and water. The position of a mountain gives some idea of its rock structure, and its rock structure and form tell something of its age. The presence of hard rock in a mountain is often shown by the upright peak whose faces may be compara tively bare, but which points up, resisting wind and water. Pike's Peak is granite rock. The White Mountains. N. H., have many hard rocky peaks; the Matterhorn, in the Alps, is a hard crystalline rock. and some of the Alaska peaks are examples of almost unyielding formations that appear to defy the ages. Remarkable ex amples of the sculpturing of the mountains by water are shown in the gorges in the Rocky Mountains, the removal of soft layers leaving the hard rocks standing like gigantic castellated ruins. The high. sharp pointed peaks and the irregular rugged surfaces indicate that the mountains are not among the oldest of the earth. The Adirondacks, with their low, rounded tops, their comparatively uniform slopes, show that long periods have passed since their formation; erosion and weathering have removed much of the ruggedness and share an gularities that once existed. Along the Atlantic Coast east of the Appalachian Mountains the low round hills are remnants of what were once high mountains. If given sufficient time, erosion will reduce the highest mountains to low featureless plains.
The mountains of the world are distributed with remarkable uniformity. The longest and highest ranges of North and South America face the Pacific Ocean, and extend almost due north and south. The longest and highest
ranges of Eurasia extend nearly east and west. Starting from the highest plateau in the world, Pamir, in Asia, there are extending west, mountain ranges which are continuous through Europe to the Atlantic, and, also, with but few low depressions, along the eastern coast of Africa to Cape of Good Hope. Passing east from the plateau of Pamir are lofty mountain ranges extending to the northeastern part of Asia, which crossing to Alaska, unite with the great ranges which skirt the western coast of the Americas. The highest mountains in the world are the Himalayas; the highest peak, Mount Everest, is fully 29,000 feet high.
High mountains exist on the bed of the ocean. A number belonging to the submerged Atlantic continent have been located. and their elevation determined. Some of the most promi nent are Mount Chaucer, located in 1850, in lat. 42° 50', long. 28° 50', crest 284 feet from the surface; Mount Sainthill, in lat. 42° 50', long. 42° 20', discovered in 1832, height about 11,000 feet. Another important submarine mountain is the Laura Ethel, discovered in 1878, its crest about 216 feet below the surface. A group of submarine mountains, in lat. 43°, long. 22° 30', has been named Edward the Seventh Range. Other Atlantic peaks are Tillot ston, Bright, Placentia and some in lat. 45° and long. 48°. Mount Placentia is only about 30 feet below the surface.
The mountains of the world are the great depositaries for the world's mineral wealth. The large proportion of the valuable metals in general use in the world have been obtained from the mountains. This is probably due to the close relation between mountains and igneous activity. (See ORE DEPOSITS). Moun tains affect the climate by protecting from cold winds or by preventing the ocean breezes from cooling the interior of countries in tropical regions, and by controlling in a great measure the rainfall. (See CONDENSATION). The flora and the fauna, so dependent upon climate, are modified greatly by the mountains. The ele vations are the great water-reservoirs of the world; they store almost the whole supply of water which falls on the earth's solid surface and distribute it in channels throughout the land. Lakes and springs are common in moun tains. These elevated land masses of the earth have been most important in determining the history of the world. They are natural bound aries, they have protected the weak from the strong, the civilized from the savage, and many sturdy, powerful races of to-day owe their early preservation in a great degree to the mighty natural barriers which stood between them and a stronger and more ferocious race. The mountains of the world have affected the literature and art of the world, and these influ ences are still felt wherever a mountain uplifts its crest.
Reade, T. M., (The Origin of Mountain Ranges' (London 1886) ; Willis, B., Thirteenth Annual Report, United States Geological Survey, Washington, D. C. (1893) ; Russell, I. C., Fourth Annual Report, United States Geological Survey (1884) ; Geike, `Mountain Architecture) ; Geikie, J., 'Moun tains, their Origin Growth and Decay' (New York 1914)) ; 'Earth Reclus, 'The History of a Mountain) ; Elie de Beaumont, 'Notice sur les Systemes de Montagnes' (Paris 1852).