109 



square foot containing on an average from 75 to 100 plants. Asso- 

 ciated with it are numerous plants of the blowsand association : 

 Diodia teres, Aristida tuberculosa, Croton glandulosus, var. scptcn- 

 trionalis, Linaria cauadciisis, Mollugo verticillata, Cypcrus Sclra'ci- 

 nitzii, and Euphorbia corollaia. The presence of these accessory spe- 

 cies is probably correlated with the thin deposit of fresh sand, since 

 they are not found on the soil layer proper. A blowout of the same 

 type in the Ocjuawka area (PI. XI, Fig. 2) is about 80 Iw 100 feet 

 (25 by 30 m.) in size, but less than three feet ( i m.) deep. Most 

 of the broad flat basin is covered with a black crusted soil layer and 

 occupied by large numbers of Stcnophylhis and a few plants of Gna- 

 phalimii polyccpJialum and Lactuca scariola, var. intc grata. There 

 are also tw^o circular patches of an unknown moss, probably only 

 two or three years old. Parts of this basin are still covered with a 

 thin layer of sand, on which the vegetation is the usual blowsand 

 association, characterized especially by Ccnchrus carolinianus, Froe- 

 lichia -floridana, and Paspahnu sctaccuui. Stabilization has already 

 begun with Lcspcdc::a capitata and Oenothera rlioinbipctala, and at 

 one end are a few plants of Populus deltoides. 



It seems probable that this association is finally succeeded by a 

 prairie vegetation, although no evidence of this was seen during the 

 present investigation. According to Gleason (Hart and Gleason, 

 igoy: 168) it may be followed in the Havana area by Cladonia and 

 Antennaria, and later is converted into "prairie, scarcely distinguish- 

 able, in vegetation at least, from the typical prairies of central Illi- 

 nois." 



The Swamp Formation 

 the saeix and soeidago associations 



Blowouts may become so deep that thev reach and uncover moist 

 layers of sand, probably not far abo^'e the water-table. In these, 

 new plant associations soon appear, which may be even hydrophytic 

 in nature. The few cases observed have not made it possible to 

 determine the order in which the vegetation develops, and the dis- 

 cussion must be limited mainly to the simple description of condi- 

 tions as they are. Cowles has mentioned a similar succession at the 

 head of Lake Michigan (iSpp: 308). 



The deepest of the excavations, measured by the vegetation 

 rather than by actual dimensions, is in the "Devil's Neck'' north of 

 Topeka, in the Havana area. The center of the depression is a 

 sandy loam and probably represents the subsoil, the Miami loam of 



