Evolution OF THE EARTH

Modern Geology regards the earth as it now exists as the outcome of a long series of proce es, the tracing of which is the ultimate and highest aim of the science. Evolution teaches that the globe was originally part of a vast ma of nebulous matter, from which, by the action of inherent laws, have been slowly developed the spheres of which the solar system consists. These at their first condensation existed as globes of liquid matter, resembling furnace slag. By subsequent cooling they have since become more or le solid, but most of them, the earth included, probably retain some of their original fluidity. A high internal temperature is indicated in the case of the earth by the phenomena of wells and deep borings, which are always warmer at the bottom than at the top. The earth was formerly regarded as a shell of solid matter surrounding a liquid core. Afterward the theory was advanced that the whole globe was solid. But the conception that best explains the phenomena manifested at the surface is that the central part is solid in consequence of the pre ure of the ma es above it at a temperature as high as is consistent with solidity, and that the surface is solidified by cold, while between these exists a liquid, or at least a viscous layer, perhaps of no great thickne . The development of the earth has been practically a long proce of slow refrigeration, which still continues; to this cooling and the nece ary contraction that follows it are due many of the superficial features of the globe. The outer crust, long cold and hard, is unable to yield as the internal portion becomes colder and shrinks. It is consequently crumpled into folds and flexures, as the skin of an orange or apple when the fruit dries. To this cause many geologists ascribe the origin of those anticlinal axes out of which by subsequent erosion our mountains have been sculptured. (See OROGRAPHY.) Another party maintains that this cause is insufficient, and that some other must exist that will afford a greater amount of shrinkage, such as the extrusion of matter by volcanoes. In either case there can be no doubt that the earth is now much smaller than it once was, evidence of immense contraction existing at the surface. by the The history of our globe consists therefore of a long and distant past, during which it was untenanted on account of the heat; a time when life became po ible and actual, the present: and a long and distant future when, owing to refrigeration and the consequent absorption of the air and the water by cooled crust, life will become again impo ible. As the first of these three stages seems to be represented by the planets Jupiter, Saturn and the Sun, which are still luminous, so the Jast is apparently foreshadowed by the Moon, which is seemingly cold and lifele , without air and water.