The Classification of Geographic Forms hy Genesis. 31 



and classified empirically, and can be referred to their proper 

 places in a genetic taxonomy without change in terminology. The 

 volcanoes, craters, calderas, lava fields, tuff fields, tufa crags, 

 mesas, volcanic necks, dykes, etc., however modified by degrada- 

 tion, alteration, glaciation, or wind action, exhibit characteristic 

 forms which have often received names indicative of their origin. 

 The glacial di-ift with its various types of surface, the moraines, 

 drumlins, kames, roches de moutonnees, rock basins, kettles, lacus- 

 tral plains, aqueo-glacial terraces, loess hills and plains, etc., have 

 been studied in their morphologic as well as their structural 

 aspects, and the elements of the configuration commonly assumed 

 have been described, portrayed, and appropriately named ; and 

 they take a natural place in the classification of products by the 

 processes giving rise to them. The dunes, dust drifts, sand 

 ridges, etc., and the wind-scooped basins with which they are 

 associated, are local and limited, but are fairly well known and 

 fall at once into the geuetic classification of forms and structures. 

 But all of these geographic forms are modified, even obliterated, 

 by the ever prevailing process of gradation, which has given ori- 

 gin to nearly all of the minor and many of the major geographic 

 forms of the earth. The forms resulting from this second great 

 category of geologic processes have generally engaged the atten- 

 tion of systematic students, but their prevalence, variety and 

 complexity of relation are such that even yet they stand in great- 

 est need of classification. 



Lesley thirty years ago regarded the mountain as the funda- 

 mental topographic element; Richthofen recognizes the upland 

 and the plain (" aufragendes Land und Flachboden") as the 

 primary classes of configuration comprehending all minor elements 

 of topography; Dana groups topographic forms as (1) lowlands, 

 (2) plateaus and elevated table lands, and (3) mountains ; and 

 these related allocations are satisfactory for the purposes for 

 which they are employed. But the implied classification in all 

 these cases is morphologic rather than genetic, and is based upon 

 superficial and ever varying if not fortuitous characters ; and if 

 it were extended to the endless variety of forms exhibited in the 

 topography of different regions it would only lead to the dis- 

 crimination of a meaningless multitude of unrelated topographic 

 elements. 



In an exceedingly simple classification of geographic phenom- 

 ena, the primary grouping is into forms of construction dmdifoi'ms 

 of destruction ; but it is evident on inspection of the table intro- 



