This magnificent tower of igneous rock three hundred feet in height has been called by some a volcanic neck. Is the direction of the columns that which would obtain in the cylindrical pipe of a volcano? The tower is probably the remnant of a small laccolith, an outlying member of a group of laccoliths situated not far distant] The Interior Condition of the Earth and Causes of Vulcanism and Deformation The problems of volcanoes and of deformation are so closely connected with that of the earth's interior that we may consider them together. Few of these problems are solved, and we may only state some known facts and the probable conclusions which may be drawn as inferences from them. =The interior of the earth is hot.= Volcanoes prove that in many parts of the earth there exist within reach of the surface regions of such intense heat that the rock is in a molten condition. Deep wells and mines show everywhere an increase in temperature below the surface shell affected by the heat of summer and the cold of winter,--a shell in temperate latitudes sixty or seventy feet thick. Thus in a boring more than a mile deep at Schladebach, Germany, the earth grows warmer at the rate of 1° F. for every sixty-seven feet as we descend. Taking the average rate of increase at one degree for every sixty feet of descent, and assuming that this rate, observed at the moderate distances open to observation, continues to at least thirty-five miles, the temperature at that depth must be more than three thousand degrees,--a temperature at which all ordinary rocks would melt at the earth's surface. The rate of increase in temperature probably lessens as we go downward, and it may not be appreciable below a few hundred miles. But there is no reason to doubt that _the interior of the earth is intensely hot_. Below a depth of one or two score miles we may imagine the rocks everywhere glowing with heat. Although the heat of the interior is great enough to melt all rocks at atmospheric pressure, it does not follow that the interior is fluid. Pressure raises the fusing point of rocks, and the weight of the crust may keep the interior in what may be called a solid state, although so hot as to be a liquid or a gas were the pressure to be removed. =The interior of the earth is dense and heavy.= The earth behaves as a globe more rigid than glass under the strains to which it is subjected by the attractions of the sun and moon and other heavenly bodies. The jar of world-shaking earthquakes passes through the earth's interior with nearly twice the velocity with which it would traverse solid steel, and since the speed of elastic waves depends on the density and elasticity of the medium, it follows that the globe is as a whole more dense and rigid than steel. _The interior of the earth is extremely dense and rigid._