During the winter of 1886-'87 Prof. W. M. Davis delivered a course on Problems in Physical Geographic Classification, treated of in two lessons, and the Laws of the Evolution of the Principal Topographical Types occupied the remainder of the course. Professor Davis gave the class the benefit of the results of his investigations, which were original contributions of importance to the progress of physical geography. "The graphic manner of illustrating the lessons upon the Glacial period and the effects of the great glacier upon the area of the Great Lakes was very effective. This was shown by means of a relief model whose surface was composed of an ingenious arrangement of overlying and differently painted surfaces. By removing these in succession the lecturer traced the whole history of changes following upon the recession of a continental glacier and its effects upon the surface waters.... These lessons were so novel and useful to teachers that he was invited to give a course of ten lessons during the next winter upon the physical geography of the United States. New matter, new models, and more extended illustrations were used in this course. The objects of the course were: To illustrate the value of systematic classification in the study of physical geography in order that forms of similar origin might be grouped together; to advocate the importance of studying the evolution of geographic forms in time, so that forms similar in origin but dissimilar in age (and consequently in degree of development) might be regarded as their natural relations; to apply these principles to the physical geography of our own land; and, finally, to promote the use of models in geographic teaching. The different parts of the country were considered in this order: The mountains as constituting the framework of the continent, the plains and plateaus flanking the mountains, the rivers carrying the waste of the land into the ocean, the lakes temporarily interrupting the transportation of waste to the ocean and retarding the action of the rivers, the shore line where the land dips under the sea."