320 LL. Lesquereux on the Origin and Formation of Prairies. 
me prairies, especially in Minnesota, the process of forma- 
tion of the prairies is repeated in the very same wa 
dominant winds. Or it is shaped as a low range of hills sur- 
rounding the lakes, and is due then to original irregularities of 
the surface. The materials are the same as those of the dams, 
or low islands, of the great Jakes; indeed, the same as those 0 
the under bottoms of the swamps, or those over which the prat 
ries have been formed. But they have been removed from the 
influence of stagnant water: this is the only difference.” 
“From all these remarks, what other conclusion can we de- 
duce but that all the prairies of the Mississippi valley have been 
formed by the slow recession of sheets of water of ease 
tent, first transformed into swamps, and, by and by, drained an 
dried. The high and rolling prairies, the prairies around - 
: a 
and as there is some unevenness of surface, have these un of 
tions not been formed like the low islands or high besa 
the lakes, and why then are they not timbered ?”—‘I _ ot 
that, although the surface of the prairies may be now undu a 
it was originally horizontal enough to form shallow lakes, f 
* Especially Planorbis trivolvis, P. lentus, Lymnea appressa, L. emarginata, * 
— sae y, etc. The lakes have the same species, ag many bivalves, — 
great.abundance of fishes, especially .catfishes (Pimelodes). 
: arent this Journal, nie, i819, and aes ibid., ii, 30, 1820, pes be 
mdered the prairies as originating from 
explanation of Die phenomencn. 
swamps, without, however, iving ® 
