At the last meeting of the Boston Scientific Society, Professor George H. Barton spoke in a very interesting "way on "Volcanoes," his paper having been called forth by the recent events in the way of eruptions and earthquakes. In outlining his subject Professor Barton called attention first to the changes which had taken place in the definition of volcano within the past wenty years and again to the latest conceptions of he sructure of the earth. "When I went to school," said the speaker, "we were taught that a volcano is a mountain that sends forth fire, smoke and lava. The latter day definition considers it not to be necessarily a mountain, nor does fire or smoke issue. A volcano, in our recent terminology is a vent in the earth's surface from which lava comes forth." The ashes which the volcano sends forth may fall about the lava and form a cone, or the lava itself may be heaped up in pyramidal form, but these mountain forms are incidents and not necessities.
Professor Barton gave in condensed form the nomenclature of the different layers of the earth, names which will be new to the generality of readers. The central portion of the earth is a hard mass about which practically nothing is known. It is believed to be firm and is of high specific gravity, higher, for example, than steel. This portion of the earth is denominated "cen-trosphere." Outside of the centrosphere lies the "litho-sphere," the rocksphere, of Which we know much and very little. The outer part of this, the ground we walk upon has been very closely studied and we know a great deal about it, and through it about the adjacent portions near the surface. But this knowledge is limited to portions of the earth at or near the surface. The "hydrosphere" is the mass of water covering a great portion of the earth's surface, the ocean, and the atmosphere is the medium in which we live. The "hydrosphere" and the atmosphere are important in geology from the effects which they have had in modifying the conditions of the surface, the water by direct erosion ana the atmosphere by the more insidious processes of weathering, fracturing by heat and cold, separating by frost action, erosion by the running water and chemical actions of various kinds, For convenience the "litho-sphere" is divided into two zones, the fracture zone, which is the outer part, and the flowage zone, which is the inner one. In the latter the rocks are under such enormous pressure that they become plastic and flow about into cavities as ice can be made to do at the surface, in the fracture zone the pressure is less and breaks and fissures in the rocks are important features in many of the phenomena.
Professor Barton then pictured the condition of the materials below the surface where under great heat and enormous masses of rock material exist. The igneous granites, for example, were such rock masses beneath the surface and wherever they are now found at the surface it presupposes that there formerly existed above these masses from five to ten thousand feet of earth or rock which has been removed.
Professor Barton then went on to the direct consideration of volcanoes, illustrating every point in their development and eruption by means of fine lantern views. The steam clouds of Vesuvius at its recent eruption, driven by the enormous force into the air for a hundred miles or more, and similar clouds on Pelee were particularly striking. The speaker's own experience with volcanoes had been in the Hawaiian Islands, which show different types, containing among others the largest crater on the earth, which while not comparable with those of the moon, still has a diameter of more than thirty miles and a depth of two thousand five hundred feet. All of the varied phenomena, the eruption, the flowing lava, the lava sprouts of fiery red, molten lava, of which he has seen at one time more than a score, the roughness of the lava bed, the smoothness of its satin-like finish, the cinder cone, all were noted and explained.