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POPULAR SCIENCE MONTHLY. 



cality in the section under consideration formed the subject of a 

 separate lesson, in which its structural features and the more im- 

 portant events of its history were presented. Special attention 

 was given to tracing the relations of the existing surface features 

 of each district to its geological structure, thus connecting the 

 physical geography and geology of the region. These lectures 

 were based on a large amount of original investigation and 

 results reached by Professor Crosby in his studies of the Boston 

 basin." 



During the winter of 188G--'S7 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. Pro- 

 fessor Davis gave the class 

 the benefit of the results of 

 his investigations, which were 

 original contributions of im- 

 portance to the progress of 

 physical geography. " The 

 graphic manner of illustrat- 

 ing the lessons upon the Gla- 

 cial 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 ar- 

 rangement of overlying and 

 differently painted surfaces. 

 By removing these in succes- 

 sion the lecturer traced the 

 whole history of changes fol- 

 lowing 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 in- 

 vited 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 



WILLIAM II. NILKS. 



