A second objection is, the vast difference in the character of lavas, even in districts very near each other. Thirdly, there seems no definite connection between volcanoes in the same region. Two adjacent ones may exhibit very different conditions. Mauna Loa is about 10,000 feet above Kilauea, a great crater of the same mountain. Yet the upper is often in a violent state of eruption when the latter is perfectly quiet. It would be difficult to conceive how these are supplied from the same source. If the interior were a molten mass in a state of equilibrium, as would be necessary if the uniformity of its motions in the solar system were to be preserved, any undue pressure would compel the molten matter to escape from the lowest opening. This would be in accordance with the simplest laws of liquids. Then we should find volcanic action most vigorous at the lowest active volcano; but such is not the case. The idea of a uniformly liquid interior seems hardly tenable.
There is still other objection to this theory. Experiments have been made with various materials to ascertain the change affected in them by heat. It is found that a block of granite five feet long, by a change of ninety-six degrees in temperature, is expanded .27792 of an inch; crystalline marble, .03264; sandstone, .0549. If, then, a portion of the earth’s crust ten miles in thickness be heated six hundred degrees, its crust would be raised two hundred feet; or a change of one degree, the rate of expansion being fairly uniform to five hundred or six hundred degrees, would raise the surface four inches. How important this matter is may be better understood when we consider that if the interior of the earth be a uniformly molten mass, with a crust ten miles thick, a contraction of one-twelve thousandth of an inch should force out of the crust a cubic mile of lava. We should find then a change in temperature one forty-eight thousandth of a degree should effect this, if the crust were ten miles thick.
We are then forced to conclude that the earth is not cooling to any appreciable extent; or that the liquid interior is still capable of indefinite compression without necessarily being forced out through orifices in the crust; or that the interior is not a uniformly molten mass.