CHICAGO AND VICINITr. 65 



ridges. The shrub undergrowth is commonly sparse, and the most 

 frequent members of this stratum are the hazel {Corylus Americana), 

 Rosa, the New Jersey tea {Ceanothus Americanus), Salix humilis, the 

 low blueberry (Vaccinium P ennsylvanicum), and the huckleberry (Gay- 

 lussacia resinosd). Among the commoner herbs are Siiene stellata, 

 Antennaria plantaginifolia, Heuchera hispida, Rumex Acetosella (Field 

 sorrel) Carex Pennsylvanica, Potentilla argentea (Silvery cinquefoil), Poa 

 compressa, Pteris aquilina (^xak€), Ceratodon purpureus. In open places 

 there are often almost pure growths of Poa or Potentilla. Figs. 34 

 and J5 show portions of these ancient beaches in which the oaks 

 dominate; fig. 34 shows, perhaps, the more common condition, i. e., 

 a rather low beach with a sparse tree growth. 



The future of the vegetation on the established dunes and beaches 

 is somewhat problematical. From analogy with other plant societies 

 in this region, and from established dunes in Michigan, we should 

 expect a mesophytic forest, probably of the white oak-red oak-hickory 

 type at first, and then followed by a beech-maple forest. There are 

 evidences that some such changes are now taking place. On many 

 of the oak dunes, especially where protected from exposure, there is 

 already a considerable accumulation of humus. Herbaceous ravine 

 mesophytes, like Hepatica, Arisaema, and Trillium, are already present, 

 and with them mesophytic shrubs and trees, including the sugar maple 

 itself, though the beech has not been found on the dunes of our area,, 

 as it has in Michigan. One might expect that the flora of the older 

 Glenwood beach would have advanced more toward the mesophytic 

 stage than has the flora of the younger Tolleston beach. Such,.indeed, 

 seems to be the case, especially at Glenwood, where the white oaks are 

 more numerous, and the black oaks much larger and more luxuriant; 

 The humus is richer, and most things look as if the age of this beach 

 were notably greater than that of the Calumet or Tolleston beaches. 

 This subject, however, needs much further investigation. In any event, 

 one character of the 'sand hill stands out in bold relief, viz., its great 

 resistance to physiographic change. Not only is its erosion slower than 

 that of the clay hill, but the advance of its vegetation is vastly slower 

 at all points along the line. The slowness of humus accumulation 

 accounts for this, perhaps, more than all else. 



