VALLEY OF THE MINNESOTA RIVER. 575 
sloughs, marshes and occasional swamps break the general 
monotony. In spite of the preponderance of the rolling 
prairie the diversity of conditions in the valley as a whole 
permits it to maintain a fairly diversified flora. 
Soils. In view of the lack of any systematic analyses of 
soils in the Minnesota valley it is possible to speak only in 
general terms of the various conditions that may be discovered. 
Practically the whole of the valley is covered with glacial 
drift and this consists of a mixture of sand, gravel, clays and 
boulders. Cretaceous clay is the most abundant component of 
the soil. This matrix is covered over with a mantle of black 
soil, resulting from the decay of unnumbered generations of 
plants, and from six inches to three feet in thickness. 
Throughout the bottomland of the main gorge the 
general thickness and fertility of the soil is most noteworthy. 
In the region of metamorphic rocks above Fort Ridgely this 
thickness diminishes in places, but to the head of the gorge 
areas of maximum thickness may be discovered. On the roll- 
ing prairies the soil is scarcely different in general character, 
so far as concerns the growth of plants. The matrix is for 
the most part of unmodified drift, while in the main gorge and 
at other points, the substratum often consists of modified or 
stratified drift. Boulders are very rare in the basin of the 
Minnesota, their area of frequency being confined to the north- 
ern and morainic portions. The clays are of the ordinary sort 
found in Minnesota glacial till. Blue and red clays are predom- 
inant. In some portions of the valley saline and alkaline soils 
are found, but such areas are small and are confined for the 
most part to the western and southwestern areas. No char- 
acteristic saline or alkaline marsh occurs in the valley, al- 
though several in which the water is somewhat brackish have 
been noted. The saline or alkaline areas are commonly 
marked enough to favor the development of characteristic 
plants, such as various Chenopodiacece and Polygonacee. 
The soils are classified by N. H. Winchell into seven groups 
as follows: (1) Red till soil; (2) gray till soil, timbered; (3). 
gray till soil, prairie; (4) loam with gravelly subsoil; (5) lami- 
nated clay soil and subsoil; (6) sandy soil with sand or fine 
gravel as subsoil; (7) alluvium. This is a geological classifica- 
tion, but may serve in the absence of any based on other char- 
acters. From a chemical point of view the data are not at 
hand to make the classification which would be the most useful 
to the botanist. Of the groups of soils named above the gray 
