12 



VICTOR E. SHELFORD. 



value of tin- principles of physiography as outlined in the fourth. 



\Yith the development of the ideas of genetic physiography 



came I lu- recognition of the succession of physiographic conditions 



over a ijveii locality (point B of Fig. i). The relations of plants 



! animals to physiographic features being recognized, the first 



recognition of plant and animal succession came in connection 



with physiographic succession. Cowles ('01) carried out a 



complete classification of the vegetation near Chicago on the 



basis of the plant succession which accompanies physiographic 



// G F E D C 



B 



FIG. i. A diagram showing the successive stages in the profile (general shape 

 of the bottom) of a very young stream, curved lines, AB, AC, A-D, A-E, A-F, 

 .1 (/. .1 // representing the successive profiles. The uppermost horizontal line 

 represents the surface of the land into which the stream is eroding. The horizontal 

 line with the arrow heads indicates the direction of the migration of the source of 

 the stream and accordingly of similar stream conditions. The vertical line with 

 arrow heads when followed downward passess through a succession of stream condi- 

 tions and represents physiographic succession at the locality B. The point A is the 

 mouth of the stream. Opposite this are shown three successive sizes of the stream, 

 and therefore succession at that point. The vertical scale is greatly exaggerated. 



change. Adams ('01) also discussed in general geographic terms 

 the relations of animals to base-leveling and stream development. 

 He referred to succession of forms in streams. Since his paper, 

 little has been done in the study of the actual relations of animals 

 to the various stages of stream development, or the relative 

 importance of the activities of the animals and the dynamics of 

 -t reams in determining distribution. 



In the study of all phases of distribution, animal activities 

 have been usually eiiher ignored or taken for granted. Tax- 

 onomy has been the center around which all such work has rotated 

 and the taxonomic characters used have been very generally 

 -tructural. In the study of succession this ha-> been true, only 



