Geographic Methods in Geologic Investigation. 11 



GEOGRAPHIC METHODS IN GEOLOGIC 

 INVESTIGATION. 



By W. M. Davis. 



Definition of Geography and Geology — Geographic Methods in Geology — Hutton 

 and Lyell — Marine deposits explained by existing processes reveal the history 

 of the earth — American Topographers — First Pennsylvania Survey ; geographic 

 form as the result of extinct processes— Western Surveys; geographic form 

 explained by existing processes reveals the history of the earth — Deductive 

 Topography — Comparison with Palceontology — Geographic Individuals — Classi- 

 fication according to structure — Ideal cycle of regular development — Interrup- 

 tions in the Simple Ideal Cycle — Geography needs ideal types and technical 

 terms — Comparison with the biological sciences — Teaching of Geography — The 

 water-falls of Northeastern Pennsylvania as examples of deductive study — 

 Systematic Geography. 



The history of the earth includes among many things an 

 account of its structure and form at successive times, of the pro- 

 cesses by which changes in its structure and form have been 

 produced, and of the causes of these processes. Geography is 

 according to ordinary definition allowed of all this only an 

 account of the present form of the earth, while geology takes all 

 the rest, and it is too generally the case that even the present 

 form of the earth is insufficiently examined by geographers. 

 Geographic morphology, or topography, is not yet developed into 

 a science. Some writers seem to think it a division of geology, 

 while geologists are as a rule too much occupied with other mat- 

 ters to give it the attention it deserves. It is not worth while to 

 embarrass one's study by too much definition of its subdivisions, 

 but it is clearly advisable in this case to take such steps as shall 

 hasten a critical and minute examination of the form of the 

 earth's surface by geographers, and to this end it may serve a 

 useful purpose to enlarge the limited definition of geography, as 

 given above, and insist that it shall include not only a descriptive 

 and statistical account of the present surface of the earth, but 

 also a systematic classification of the features of the earth's sur- 

 face, viewed as the results of certain processes, acting for various 

 periods, at dijfferent ages, on divers structures. As Mackinder of 

 Oxford has recently expressed it, geography is the study of the 



