Recent investigations appear to have shown that terra firma is a phrase indicating a condition of our solid earth which scientifically has no existence. The crust of the earth is in a state of constant movement. When these movements are sudden and violent, we call them earthquakes; transient shiverings, which require the aid of instruments to make them visible, we call earth tremors; movements of longer period and greater amplitude, causing large areas, like islands and continents, to rise and fall like rafts upon the ocean, are called oscillations. To express the study of the whole of these Earth-movements it would here be convenient to have a special term.