L. Lesquereux on the Origin and Formation of Prairies. 321 
_ then swamps, like those which at the present time cover some 
_ parts along the shores of Lake Erie, Lake Michigan, etc. Where 
_ this horizontality has disappeared, it is only by very slow de- 
_ grees, under the eroding action of water, which, in its slow 
- movements, tends to follow every change of level, seek an out- 
_ ket, and so establish channels of drainage. I have followed for 
_ whole days the sloughs of the prairies, and have seen them con- 
_ stantly passing to lower and well marked channels, or to the beds 
of the rivers, by the most tortuous circuits, in a manner com- 
- parable to the meanderings of some creeks in nearly horizontal 
valleys. Indeed, the only difference is, that, in the high prairies, 
there is not a definite bed, but a series of swamps, extending, 
_ harrowing, and bending in many ways. The explanation ap- 
_ pears to me so natural, that I cannot understand how high prai- 
_ Nes could ever be perfectly horizontal. Along the lakes and 
_‘Mtheir vicinity, the horizontality is a necessary consequence of 
the primitive evenness of the bottom and of the proximity to 
water. The level of the low prairies being scarcely above that 
Of the lakes, their surface, after an overflow, becomes dry, rather 
percolation and evaporation than by true drainage. But 
_ “erever the rivers have cut deeper channels,—as is the case in 
the north part of the Mississippi basin, where they run some- 
| from one to three hundred feet lower than the surface of 
: the high prairies—the drainage has constantly taken place to- 
_ Ward those deep channels, and the water, though its movements 
_ May be very slow, furrows the surface in its tortuous meander- 
rom this, results that irregular conformation of surface 
: generally and appropriately called rolling. In Indiana and Illi- 
‘TOs, in the vicinity of the Wabash river, for example, there 
 & some high prairies whose surface is apparently horizontal. 
| Bat hese prairies, as at Terre Haute, are surrounded by a mar- 
gin of low wooded hills, and have originally been shallow lakes 
_ ‘ Giicult and slow drainage. Moreover, their horizontality is 
“ther apparent than absolute; some parts of them are already 
2 ary enough to be cultivated and ploughed in the spring; oie 
~ are used as wet meadows, and still others are covere 
| With Water and inaccessible. This apparent horizontality results 
aM the great width of what we may call already channels of 
iinage. These will, by and by, contract and deepen, and thus 
. Prairie become undulating. This opinion is in 7. 
| r What you say in your excellent paper on the drift of m e 
Retior: that the irregularities of surface of the prairies have 
caused by currents at the time when they were under 
Water. If the ground of the high rolling prairies had been 
: Mea in advance, as you ri te the ap bad bbe re 
| tela would have been timbered like the low isla 
