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 GhenopodiacecB and Polygonacece. 



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. Prom 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 



