128 VICTOR E. SHELFORD. 



MOII. Ecolojiif.il Micce ion is succession of ecological types 

 regardless of species, while geological succession is the succession 

 of species. Tin- data presented here affords an excellent op- 

 portunity to bring out the differences and relations of these two 

 types of succession. 



\Ve noted also in the first paper that the first recognition of 

 plant and animal succession came with the development of 

 genetic physiography. It was mainly the successsion which ac- 

 companies physiographic change. Cowles ('01) also clearly 

 recogni/ed succession due to the action of plants themselves. 

 Tin- l.n ler idea has been elaborated by Clements ('05) and essen- 

 tially demonstrated by Schantz ('06) and Dacknowski ('08). 

 Animals must obviously play an important role in this type of 

 succe ion. |,ut unfortunately this has not been investigated. 



The succession with which we will deal in this paper is that 

 n--ulting fron the action of organisms on their own environment. 

 For all practical purposes the area selected for this study has 

 been in a condition of physiographic stability for a considerable 

 period. The selection and analysis of the place of study is the 

 most important step in the whole investigation. Indeed there 

 are only a few suitable localities in North America. 



II. AREA OF STUDY. 



Owing to the fact that succession is always either dependent 

 upon, or modified by changes in conditions, a correct interpreta- 

 tion of this phenomenon depends largely upon accurate kno\\ ledge 

 of the area under consideration. 



I. Location and General Character. The ponds which are tin- 

 subject of this study lie in the sand area at the south end of Lake 

 Michigan, within the corporate limits of the city ot (iary, I ml. 

 They maybe reached from stations known as Pine, Buffing ton, or 

 Clark Junction. This locality is characterized by a large series 

 of sand ridges, for the most part nearly parallel with the lake shore 

 (Map I.). Their average width is about 100 feet. They are M-pa- 

 rated by pond- \\liich are someuhai narrower (Map II.. p. 131). 

 Most of these ponds are several miles long. The\ \ar\ in depth 

 during the spring high water, from a few inches to four or live 

 feet. They describe an an- somewhat longer than the lake shore 

 (Map I.), and are farthest from it about midwas of their lengths. 



