The study originally prepared at the writer's own institution was revised and greatly enlarged on the basis of materials available only in European libraries. That the writer was able to use these materials resulted from the fact that he was studying another project, in Europe during the year 1938-39, enabled to do so, in part, by a grant from the Social Science Research Funds of the University of Minnesota.
Appreciation should be expressed for the cooperation of the library staffs at the Universities of Vienna, Zurich, and Clark, of the National Library at Vienna, and particularly of the Geographical Institute of the University of Vienna. At each of these libraries publications were found that were not available at any of the others, nor in the library of the writer's own institution.
The privilege of attending the "Oberdeutschen Geographentag" at Isle Reichenau, April 1-5, 1939, enabled the author to receive helpful suggestions from German and Swiss geographers attending those meetings. Similarly the author is indebted to a number of other European geographers, most especially to Professor Johann Sölch. He wishes also to express his gratitude to the editor and to the anonymous critics of the ANNALS whose assistance far exceeded the requirements of their positions.
In the last analysis, the value of the study rests on the works, both those expressly methodologic and those illustrative of methods and philosophies, of the geographers, numbering nearly two hundred, whose publications provided the material from which my monograph is constructed. R. H.