i 
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4 
2 
A. Winchell on the Prairies of the Mississippi Valley. 333 
cause exists. The first fact is brought into consideration under 
the first of the following propositions; the other is discussed 
under the propositions which follow the first. 
1. The soil of the Prairies is a Lacustrine Formation. 
Some of the older writers on the prairies, —_— their at- 
oat to the so-called “‘ wet prairies,” so common in Ohio and 
gan—now usually termed “marshes,” wnalea? and “bogs” 
the wide, rolling prairies of Illinois 6 contiguous states, 
the local swales of that or other sta 
The lacustrine origin of the prairie > soil is shown, /irst, by its 
physical characters. Not only has it the fineness, color and veg- 
etable constitution which characterizes such soil, but we actually 
discover in it abundant remains of lacustrine shells, disseminated. 
hundreds of miles from the present limits of the lakes. If, 
among older formations, we are ermitted to infer the origin of 
e sediments from the nature of the included organisms, the 
€vidence from testaceous remains is not less conclusive as to 
hature of the prairie sediments. 
The lacustrine origin of the soil is shown, secondly, by the 
. necessary effect of geological changes of level which are gener- 
Mie admitted to have taken place. From the head of die 
Even the increased dlevation se te on the position of ol 
ills of Niagara at Queenston—that is to say, the level of lake 
Erie at the time when the falls began to excavate their great 
Hall, York, 348, 383; Lyell, 6 Sigg in N. A. 
Vi. Visi 2, Fae: i862 Desor, Fete ee Whit Whitney's Rep. L. Sup., 204, 212, 
» 253; Hubbard, Mich. Geol. Rep., 1840, p- 102; Whittlesey, inks Journal, 
¥, 31; Logan, oe a 910, é&e. 
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