Physiographic Subdivision of the United States

Abstract

(chairman). The map herewith presented and the ac-companying table of divisions constitute the report of that committee. The same map on a larger scale (120 miles to the inch) will be found in Volume VI of the Annals of the Association of American Geographers, accompanying a paper by the writer on the Physiographic Divisions of the United States. In that paper are given the nature of the bound-ary lines and those characteristics of the several units which are believed to justify their recognition as such. Though the above-named com-mittee is not directly responsible for the statements there made, many of them represent the results of the committee's conferences. The paper as a whole is believed to represent fairly well the views of the committee, though in form the greater part of it is a revision of a former publication.2 The basis of division shown on this map, here reproduced, is physio-graphic or, as might be said in Europe, morphologic. The divisions are based on land forms, not on climate or vegetation. If subdivision were carried far enough on the same principle each unit of the lowest order would comprise but one physiographic type. In most cases this has not been done. Even the units of the lowest order generally embrace several types closely associated in their development. The genetic classification of land forms is now generally familiar to geographers, even to those who do not use it. In this system physi-ographic forms are classified according to their histories. Forms which result from similar histories are characterized by certain similar features, and differences in history result in corresponding differences of form. Generally the distinctive features which are important in a genetic classification are also obvious to the casual observer, but this is not universal. Thus a maturely dissected plateau may grade without a break from rugged mountains on the one hand to mildly rolling farm