Ill 



"western shore of Lake Michigan from Kenosha, Wisconsin, 

 down to the IlHnois-Wisconsin state hne. In that locality the 

 shore is being gradually washed away by the action of Lake 

 Michigan. The dunes were studied during 1908 and 1909, dur- 

 ing which time the complete stages of destruction of some of 

 the dunes were observed. 



To explain the formation and the stages of destruction of 

 these dunes, it is necessary to go intO' the historical develop- 

 ment of this part of the lake shore. This beach is the ex- 

 posed lake bottom and sand bars of a glacial Nipissing lake 

 which preceded the present Lake Michigan and was from 3 

 to 17 meters above it in level. Since the low-water period, which 

 ended about 1896, the rising waters of the lake have been cut- 

 ting into the beach in places and carrying the sand along the 

 beach toward the southwards. From Winthrop Harbor north 

 to Kenosha is a place where the shore is being washed away 

 fairly rapidly. When such action commences, there is usually 

 a bluff formed at the line af contact of the storm waves and 

 the beach. The bluff, however, is maintained by plants, for 

 the sand of which the soil is composed will not of itself re- 

 main in such a position. The profile of such a beach is shown 

 in Fig. 6 of the diagram. 



The plant association that is all important in maintaining the 

 bluff is the Juncus haliicus littoralis association. From 97 to 

 99% of the individual plants belong to that species of Juncus. 

 The rhizones form a very dense tangle, which not only helps 

 to protect the beach from the attack of the waves, but also 

 serves to protect the sand from desiccation, for dry sand forms 

 a gradual slope instead of an adrupt bluff. Back of the Juncus 

 balticus littoralis association is the Potentilla ansemia associa- 

 tion, a narrow zone, separating the Juncus from the grassy 

 sand plain which stretches back for many meters. As was the 

 case with the Juncus association, the facies comprises more than 

 80% of the Potentilla anserina association. The secondary 

 species which make any showing whatsoever are Monarda 

 punctata, Sporoholus cryptandrus, and Cenchrus caroUnianus. 

 Both of these grasses usually occur in the tension zone b-^twecn 



