262 



the south, are, for the most part, wider, and are occupied by prai- 

 rie rather than by marsh plants. At the IlHnois-Wisconsin state line 

 the innermost oak ridge has been cut away, leaving an area of level 

 sandy ground, one kilometer in width, from tlie lake to the bluff, in 

 which the highest elevation above Lake Michigan is scarcely 0.5 

 meter. 



Nearer Kenosha occurs the last oak ridge (PI. XLIV, Fig. i), 

 which is quite wide and has several large blowouts in its sandy soil. 

 The end of this ridge is about a kilometer south of Kenosha. 

 It is being rather rapidly cut into by Lake Michigan. A little 

 north of the end of this ridge, and protected by it on the south and 

 west, occurs the only traveling dune of this are^a. It is very small 

 in comparison with those at the head of Lake Michigan. The part 

 between the oak ridge and the railway track is a sodded, sandy plain. 



Just south of Kenosha measures have been taken to prevent the 

 rapid cutting away of the shore that had been going on. Conse- 

 quently the natural conditions have been destroyed. A little north of 

 Kenosha the Glenwood ridge has been cut into by the lake, and there 

 the region under consideration terminates. 



Associations: General Consideration 



In the naming of the ecological units there is still a confusion of 

 terms. In this article the name "association" is used to designate 

 these units; and by an association is meant a group of livmg forms 

 whose epharmony (ability to live with other forms in a given en- 

 vironment) enables them to live together as a uniform or homo- 

 geneous area of definite biotic composition. 



Although animals are not given consideration in this article, it 

 must not be forgotten that they are an essential part of the associa- 

 tion, especially the smaller animals. Their ecological relationships 

 and correlations have, in general, not been sufficiently worked out 

 to accord them their proper consideration. 



The term association rather than formation- has been used for 

 the name of the ecological unit because of its priority* and its nat- 

 ural fitness. The term formation, as originally proposed by Grise- 

 bach,f was clearly intended to connote a broader group than the simple 

 ecological units which he mentions but to which he does not apply 

 a name directly. To use the term formation as the name of the 



*HuMBOLDT, 1807. Essai sur la Geographic des Plantes, p. 17. 



tGRiSEBACH, 1838. Uber den Einfluss des Klimas auf die Begrenzung der 

 Natiirlichen Floren. Linnaea, 12:159-200. 



