Page:Popular Science Monthly Volume 48.djvu/898

816 might nearly as well be buried. The geologist who seeks, for example, the causes of volcanism, will find help in his study of the distribution and relative action of existing volcanoes—in other words, he can not keep from geography. The geographer, in his turn, needs the perspective of ancient volcanic history, if he would appreciate his own facts. Because he has commonly had no such vista, he has burdened generations of boys with the solemn blunder that a volcano is a burning mountain. Thus we may vindicate for each science its own center while granting a generous measure of common facts. The difference is in the point of view, the aim, and method of treatment; the geologist seeks largely that which has been, the geographer that which is, and each must be known in the light of the other. It is precisely the case with two biologists, one of whom studies living, the other fossil, forms. The day is past when they can work apart; yet none would deny that their fields are reasonably differentiated.

The new geography is a recent growth. Its facts and principles are little diffused and have not found their way into text-books. Thus it came about that the Conference report on geography is characterized as the most revolutionary of all those received by the Committee of Ten on secondary-school studies. Even scientific surveys of the several States do not yet show much impress of the new doctrines. Prof. Davis, the geographer of Harvard University, affirms that his students search, with meager reward, for accounts of physical features in the literature of the several States. As the same writer has truthfully said, systematic study of topography is largely American, and for the reason that the broad object lessons of the Appalachians and of the West gave our scholars the opportunity and the stimulus to lead in such researches.

The central principle of the new geography established by Powell, Button, Gilbert, Davis, and other American geographers and geologists is the doctrine of a base level of erosion as the goal of the destructive processes. Given an early "constructional "land surface, such as a newly raised sea bottom, and it will pass through what is called a cycle of development. Youth, with extended uplands and steep, narrow valleys, is followed by a much dissected, highly diversified topography marking the stage of maturity, whence is a gradual passage to the low reliefs, slight gradients, and quiet monotony of old age. During this cycle all forms of scenery have place, and in untrammeled variety, dependent upon climate and the constitution and structure of the mass upon which this land sculpture is wrought. Thus the horizontal beds of the Catskills give one type, the folded sediments of the Appalachians another, and the crystalline masses of the Adirondacks a third. Before such a cycle is completed in an actual base