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IOWA ACADEMY OF SCIENCE 105 
As has already been noted, the greater part of the surface deposits 
are of Kansan drift origin. This is a bluish clay where it is exposed 
in a thick bed, and contains numerous small boulders. However, where 
it is exposed along streams or roadsides it is usually of a red or reddish 
brown color, due to oxidation. All this drift sheet is covered by a 
thin mantle of loess, except where eroded and removed by streams. 
The valleys of the Skunk River and the Big Cedar Creek are broad, 
averaging about one mile in width in this county. Most of the surface 
of this flood plain has received a rich alluvium deposit of sand and finer 
soil particles. Big Creek also flows through a rich alluvial plain in the 
lower part of its course. The soils of the prairies are dark colored and 
vey rich in humus. 
The genus Carex is the largest of the sedge family (Cyperaceae) com- 
prising probably more than two-thirds of the species. They are a very 
difficult group because, the unisexual, monoecious or dioeeeous flowers 
offer so little variation; hence the specific characters are founded on the 
mature fruit, the character and inflorescence of the spikes, on the size 
and shape of the. achene, on the scales, and on the character and width 
of the leaves. These differences are often so slight and indefinite and 
the characters so variable, that they make the determination of species 
exceedingly uncertain. The mature fruit and the whole plant is neces- 
sary for accuracy in identification. Almost all the common species are 
sufficiently matured for study about the middle of June. 
The sedges are for the most part plants of marshes, although there 
are some notable exceptions. They form an important part of the 
vegetation in bogs and swales, and are of some economic importance on 
account of the good pasturage they afford. Those found in the uplands 
and meadows are fewer, rather scattered and inconspicuous. Likewise 
those in the woods are usually not in colonies but more or less scattered. 
Among the grasses we find many introduced species of plants which 
thrive well in their new habitat, but among the sedges this is very rare, 
none being reported thus far from Iowa. The reason is very evident, — • 
Most grasses grow under conditions very much like our cultivated plants 
and are easily distributed with seeds of all kinds. The sedges, on the 
other hand, are mostly hydrophytic, or inhabitants of woods; and! low- 
lands that are not cultivated. The xerophytic species are easily de- 
stroyed by cultivation, as nearly all the sedges are perennial by root- 
stocks. 
Distribution of seeds is accomplished by various means, but it might 
be said at the outset that the plants are usually not highly specialized 
