TIIE GEOGRAPHICAL DISTRIBUTION OF' VOL CANOES. With hardly an exception all volcanoes are situated in what can reasonably he assumed to be areas of weakness in the earth's crust, such areas being the ocean basins theniselvcs, the borderland: of these basins, n11 the mountain ranges which flank or construct the continental outlines. It follows then that volcanoes are either insular (oeeanie) or sub-oeeanic—i.e. placed on the continents close to the oceanic border, No distantly inland (active) volcano is known uncles it (.:111 be shown to be in a region of crustal instability (Southern Mexico) or One in which a emnparatively recent disruption has taken place (the volcanoes of the Creat Rift Val ley, of East Conn)] Africa—Mfumbiro Hroup). Mount Wrangel, in Alaska, is a possible exception to this rule. The main line of areas of volcanic distribution are: ( 1 ) The Pacific-Caribbean belt following the Andes of South A III erien, with many dormant, extinct, or active summits (Aeon cagua, Mistf, Cotopaxi, Sabatini. Chimborazo, Tolima) ; the Lesser Antilles Pel6e, and many peaks on Saint !Alvin, Dominica, (tuadeloupe, etc.) ; Central America aunt Mexico ( Irasn, Coseguina, Izalco, Santa Maria, Agna, Fuego, Popocatepetl, Orizaba, Colima, .lorullo) ; the West coast of North -\meriea (Shasta, 1100(1, Rainier, Baker, Wrangel, Illiatnna, Sheshal(1en, DIaknshin) ; Kamchatka, the Japanese Islands, (Fujiyama, Aso-San, II:mini-Sam As:mqy:oa ) ; the Philippines (Mayon) and Sunda Sea Islands ( Gelunggung, Pa padayang, Tengger, Temboro, Krakatoa) ; New Zealand (Egmont); and Vic toria Land (Antarctica : Erebus and Terror). All of these seem to define a nearly eontinuous line or belt of weakness or disruption in the earth's crust. (2) A Mediterranean-Caspian region is defined by the positions of the Lipari Islands (with Stromboli), Etna, Vesuvius, the -Egean Islands (with Santorin), Demavend, and Ararat. (3) An Atlantic region, defined by the mainly quiescent volcanoes of Iceland (11cda, Ska ptar Jiikull), the Azores ( l'ico), Madeira, Ca naries (Teneriffe), Cape de Verde Islands, Tristan da Cunha, etc. (4) A Pacific region, with the
numerous volcanoes on the small islands of the Polynesian group and the three main volcanoes of Hawaii (Mauna Loa, Mauna Kea, and Kilauea).
TIlE CAUSE or VOLCANIC? ERUPTIONS. There is still much obscurity regarding the causes that condition volcanic eruptions—that permit of the generation of steam within the earth's interior, of its explosive escape through the 'crust,' and of the formation or existence of the molten mag matic mass that reaches the surface as lava or in its disrupted form, as seorhe and ash. The ac eessibls facts seem to point to the conclusion that the steam or vapor of water is derived from the hydrated rocks of the earth's superficial mass, and its sudden evolution is due to release from pressure of the rock or magma with which it is inbound, or to steady and increasing superheat ing. These conditions, as well as that of the uplifting and outthrow of lava, might he supplied as the result of deep rock displacements, which, by squeezing, would bring the more highly heated deeper crust nearer to the surface or to the critical point of dismemberment. And these dis placements can readily be ascribed to vast subsi dence, notably of the sea bottom.
BuittoonArnY. Lyell, Principles of Geology, wets i. (New York, 1872) : I eikie, Tc.rt-Rook of Geology (London, 1893) ; Scrope, "Considerations on Volcanoes," Geological If a ga::in c (London, 1570) ; En ohs, Vulkane and Erdbeben (Leipzig, ; Mallet, "Volcanic Energy," Philosophical Transactions of the Royal 5ocicty (London, 1873 ; Dana, Ph a• a et eristi cs of Volcanoes (New York, 1890) ; Judd. Volcanoes (ib., 1891) ; Russell, 1'0/canoes of Yorth America (ib., 1897) : prin, .Mont Peter and the Tragcrly of Martinique (Philadelphia, 1903) : and various memoirs by Eapparenty, Bonney, Su pan, Humboldt, Von Buell, and Darwin.
See GEOLOGY: VESUVIUS; ETNA; PELEE, MONT ; etc.