tine Island, forming a part of the Big Mound, derived princi- 

 pally from Mississippi river sands (see PI. IV, figs. 1-3) ; — those 

 which are found near Adams, in the bed of the glacial Lake Cal- 

 vin, which are derived chiefly from the sands of the old lake 

 bed ; — and those which have encroached more or less upon the 

 Illinoian drift-plain north and northwest of Bayfield (see PI. V, 

 fig. 1), which are probably derived in part from the bars of the 

 Cedar river, and in part from the sandy margin of the Illinoian 

 drift. 



The dunes of the Muscatine region are largely fixed by a well- 

 developed vegetation, but portions of all these areas become de- 

 nuded at times, particularly during dry summers. 



These dunes, like those of Harrison county, are made up of 

 fine sand. 



4 — The ridge sands and gravels. — These are more limited in 

 extent, and are foimd in interrupted groups and patches, chiefly 

 along the border of the lowan drift from Hardin county east^ 

 ward to the Mississippi and along the border of the Illinoian, 

 where they blend in places with the dunes; and in limited por- 

 tions of the Kansan drift area. Similar ridges are found along 

 the border of the Wisconsin drift, especially northward in the 

 state,' and they are covered with a typical prairie flora. 



These ridges owe their sand and gravel to the several drifts, 

 and they are now mostly quite stable, and their flora blends with 

 that of the adjoining prairie or forest. 



5 — The talus sands. — These sands are very limited in area., 

 and are restricted to the vicinity of the bases of sicattered ledges 

 of St. Peter Sandstone in the northeastern part of the stae. A 

 small portion of such an area is shown in front of the ledge in 

 Plates I-III, Vol. V of this series, following p. 224 (bis) ; 1904. 



The several sand-areas are not sharply defined. The beach 

 and bar areas blend with the prairie, swamp, or forest; the dune 

 areas connect with the alluvial sands on the one hand, and with 

 prairie and forest soils on the other ; the ridge sands and gravels 

 grade into prairie and forest; and the limited talus sands like- 

 wise soon pass into forest or prairie soils. 



The Flora 



This intergradation is also reflected in the flora, which some- 

 times shows an admixture of swamp species, and at others of 



8 



