PLANT STUDIES IN LYON COUNTY 
397 
this region, the so-called Nebraskan drift, here composed of a 
dark bluish jointclay, with small angular rock fragments, very 
impervious to water, and very tough and glutinous when it is 
wet. Many springs come out of the Aftonian gravel at the 
upper edge of the Nebraskan drift. They are fed by the rains 
soaking through the permeable Kansan drift sheet. Some of 
these springs are large, one such, a little farther along the river, 
flowing a constant stream easily large enough to fill a six inch 
pipe. In the area selected slumping of soils had occurred great 
enough to cause some general mingling of the various elements 
mentioned above as composing the geological formation. The 
river bottom is quite sandy. 
On these bluffs we have the high upper hill tops exposed to 
all the winds, that blow, and not sheltered in any way. Going 
down the bluff face we pass through zones of greater and greater 
protection from the southerly winds, and in the forest the trees 
shelter the herbaceous plants, and to a considerable degree 1 one 
another, from the northerly winds, and from the sunlight. On 
t lie river bottom the shelter from prevailing winds is also as- 
sisted by heavy woods on the north of the river, and by the 
woodland up and clown stream. 
The particular tract selected for this study is in section 20. 
township 98 north, range 48 west, in Lyon township, at a point 
that I call Syverud Bluff, from the ' gentlemanly farmer who 
owned it. 
Man has exerted a minor influence on the flora of this tract. 
Some of the largest of the trees have been cut clown, and the 
bottom land and the forested bluff face have been very lightly 
pastured. 
The prairie hill top was not pastured, nor had it been culti- 
vated in the part belonging to this study. A few stray clover 
plants only have come in from a near-by field. We have here, 
therefore, an almost pure native flora. Such a pure native flora 
is a rarity in any part of Iowa, or of the states near to Lyon 
county, because the great value of the agricultural lands has 
led to the cultivation of almost all the prairie tracts, and the 
scarcity of timber has led to the destruction in large part of the 
native forest. 
On this bluff a. tract 145 feet wide from east to west, and 
running from the river south to the hill top, and extending 
