L. Lesquereux on the Origin and Formation of Prairies. 317 
Arr. XL.—On the Origin and Formation of Prairies; by LEo 
7 LESQUEREUX. 
THis paper is intended as a review of Prof. Winchell’s new 
theory on the origin of the prairies of the Mississippi Valley,’ 
—andas a defense of my own views on the same subject.’ I shall 
- therefore omit all details relative to the surface of prairies, their 
conformation and appearance, and their geological and geograph- 
ical distribution, since these details do not directly concern the 
dlucidation of the question.* | 
_ From the brief mention made of my opinion concerning the 
formation of prairies, it appears to have been misunderstood 
by those who have quoted it, or rather it was entirely unknown 
| tothem. For this reason it is advisable to first expose, as they 
Were originally given, the essential points of a simple explana- 
tion, which does not merit to be spoken of as a theory. 
48 they are raised above water. These dams are not always 
built upon the shores, and do not always even follow their out- 
: lines, but often enclose wide shallow basins, whose water 1s thus 
sheltered against any movement. ere the aquatic plants, 
sedges, Tushes, grasses, soon appear, and these basins pre 
| Thane: as may be seen near the borders of Lake Mic sane. 
hough the forests may surround them, the trees do not in a 
them, even when the swamps become drained by some natu 
eration. During a flood, the heaviest partic! 
deposited on both sides of the principal current, along = a 
- Of slack water, and by repeated deposits, dams are slowly orme 
t 
This Journal [i see 
2 2|, xxxviili, 332. 
Letter Sais tis“? + Nat. de Neuchatel, Dec. 1856. 
to Prof, Besse in Bull. de la Soc. des coe f et Geological Survey of the 
given a clear and very accurate descriptive account of the prairies 
AW Jour, Sct.—Szconp Sertms, Vou. XXXIX, No. 117.—Mar, 1865. 
41 
