In the science of material things, mechanics takes account of forces that act on masses from without; physics, of those that act from within, or which, in some way, modify the condition of the bodies themselves. Both branches were, till recently, included in the vaguely comprehensive term “Natural Philosophy,” and the partial separation observed in modern treatises and text-books gives a little more distinctness to the facts presented. Under the former the earth is contemplated as a planet, obedient to the universal law of gravitation, and moving regularly in its orbit. The mechanism of the system is complete; the measure and adjustment of all the parts perfect. GEOLOGY, As a physical science, considers the earth apart from the solar system with which it is connected, and takes account of its materials and structure, and the forces that unite them. Its position in the group is about midway between mechanics and chemistry, being closely allied to other natural sciences, while its phenomena are occasionally varied by both mechanical and chemical agents. PHYSIOGRAPHIC GEOLOGY Treats of the earth’s exterior physical features; of its form—an oblate spheroid—of its surface, oceans, continents, seas, lakes and rivers, hills, mountains, valleys and plains; of soils made from previously existing organic or inorganic substances, the detritus of rocks containing various minerals and small particles of decomposed vegetable matter. The materials of this outer covering of the earth are from many different sources, and variously constituted. From the finest grains of sand, clay, and loam, to pebbles, boulders, and fragments of enormous dimensions, they are mingled apparently without any fixed order or proportions; sometimes but slightly covering the solid rock, at others piling it up in ridges and hills of considerable height. In this surface formation are included ancient sea-beaches, lake and river terraces, deltas, deposits of sand and clay, with vast beds of marls, peat and calcareous tufa,[1] all the progressive accumulations since the present order of things began. In some of these deposits, more recent than the Drift[2] period, fossils are abundant and very full of interest. In New Zealand the bones of a bird[3] were found which exceed in bulk those of the largest horse, and are now in the museum of the College of Surgeons, London. The bird when alive was eleven or twelve feet high. Less than a century ago what might have been a fossil elephant was found imbedded in ice on the coast of Siberia, and in such a perfect state of preservation that the people fed their dogs on its flesh. The animal was well covered with hair, and adapted to a cool climate, a representative of an extinct race. How it was imbedded, or how long it had been preserved in that condition, no one knows.