344 GEORGE E. NICHOLS 



states that, "From the standpoint of the vegetation the topo- 

 graphic relations are more important than the geological. 

 . . . all kinds of soils may have the same kind of vegetation 

 when placed in similar topographic conditions, whereas the same 

 soil may show many diverse types of vegetation." 



In classifying the edaphic formations within a given climatic 

 region, topography, as related to the physiographic history of the 

 region, is of fundamental importance. For, using this as a basis, 

 it is possible to bring out the developmental relations of the 

 physiographic unit areas involved, in much the same way that the 

 classification of associations with reference to the phenomenon 

 of succession brings out the developmental relations of the 

 habitats concerned. It should be reiterated however, that while 

 the contemporaneous features of the physiography of any region 

 are the result of progressive development in the geologic past, 

 from the standpoint of present-day physiographic ecology, with 

 the exception of the relatively few areas in which changes man- 

 ifestly are taking place rapidly, the physiography can be regarded 

 as stable. That, on the whole, from the viewpoint of dynamic 

 physiographic ecology, soil is of subvsidiary importance to topo- 

 graphy in determining the character of the vegetation seems 

 obvious. But that soil may also exert a far-reaching influence 

 on the ecological character of the vegetation is emphasized by 

 the survey of vegetation set forth in "Types of British Vegeta- 

 tion" (21) where the formations are classified primarily with 

 reference to soil. In general, then, the writer would classify 

 the edaphic formations (1) with reference to topography, and 

 (2) with reference to soil. 



The edaphic formation-complex. The edaphic formations of 

 any area, taken collectively, may be regarded as an edaphic 

 formation-complex. And juet as the association-complex of 

 a physiographic unit area constitutes an edaphic formation, so 

 the edaphic formation-complex of any climatic region consti- 

 tutes a climatic formation. 



