18 National Geographic Magazine. 



a formation containing trilobites underlies another containing- 

 ammonites, but on finding the fossils in the two, confidently and 

 as far as we know correctly concludes that such is their relative 

 position. Thus the sequence of submarine processes is made out 

 by the sequence of organic forms. In brief, palaeontology has 

 passed largely from the inductive to the deductive stage. 



The geographer first regarded the features of the land as com- 

 pleted entities, with whose origin he was in no wise concerned. 

 Later it was found that some conception of their origin was im- 

 portant in appreciating their present form, but they were still 

 regarded as the product of past, extinct processes. This view 

 has been in turn displaced by one that considers the features of 

 the land as the present stage of a long cycle of systematically 

 changing forms, sculptured by processes still in operation. Now 

 recognizing the sequence of changing forms, we may determine 

 the place that any given feature occupies in the entire sequence 

 through which it must pass in its whole cycle of development. 

 And then reversing this conception we are just beginning to de- 

 duce the past history of a district by the degree of development 

 of its features. Geography is, in other words, entering a de- 

 ductive stage, like that already reached by palaeontology. 



The antecedent of deductive topography is the systematic 

 study of land geography. The surface of the land is made up 

 of many more or less distinct geographic individuals, every indi- 

 vidual consisting of a single structure, containing many parts or 

 features whose expression varies as the processes of land sculpture 

 carry the whole through its long cycle of life. There is endless 

 variety among the thousands of structures that compose the land, 

 but after recognizing a few large structural families, the remain- 

 ing differences may be regarded as individual. In a given family, 

 the individuals present great differences of expression with age, 

 as between the vigorous relief of the young Himalaya and the 

 subdued forms of the old Appalachians ; or with elevation over 

 base level, as between the gentle plain of the low Atlantic coast 

 and the precocious high plateaus of the Colorado river region ; 

 or with opportunity, as between the last named plateaus with ex- 

 terior drainage and the high plains of the Great Basin, whose 

 waters have no escape save by evaporation or high level overflow ; 

 or with complexity of history, as between the immature, unde- 

 veloped valleys of the lava block country of southern Oregon, 

 and the once empty, then gravel-filled, and now deeply terraced 



