ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 149 



P 



about 10 inches, and of subsoil (b), taken to a depth of 8 

 inches below the topsoil. The sample marked 4 was ob- 

 tained from a depth of about three feet, and is a stiff and 

 plastic clay, such as is occasionally found in the Bluff for- 

 mation in pockets or layers, anywhere and at any depth. 



"For the sake of comparison with other soils a second 

 table is calculated for perfectly dry material, and in addition 

 some data given, which are derived from treating the ignited 

 soils with muriatic acid and partially analyzing the solution. 



"The composition of these soils is so nearly uniform as to 

 warrant the conclusion that the results of field experiments 

 niade upon them cannot be influenced by any supposed 

 difference in their make up." 



In the more elevated portions of our territory, such as we 

 find in the vicinity of Jefferson Barracks and from there south 

 to the Meramec, the soil in various places is formed directly 

 upon and from the sedimentary rocks, though here and there 



to be some indications of the presence of drift. In 

 such cases the residual soil is of a rich nature, though the St. 

 Louis limestone, as indicated above, is of a rather pure 

 character. It contains a large amount of black humus but 

 has no great depth, varying in thickness from 1 to 12 inches 

 on the hills and plains. Where the plains are covered by 

 timber, the thickness of the soil layer is somewhat greater 

 than in the open. Immediately below the soil is a layer of. 

 slightly disintegrated, much broken up limestone,* through 

 which the roots of the plants penetrate, afterwards to 

 find their way through the fissures of the deeper limestone 

 layers. 



The wooded slopes of the upland portion are covered by 

 an accumulation of colluvial soil mixed with some residual 



seem 



and 



forms 



* The question whether some of this material is not of glacial origin re- 

 mains to be settled. The writer never found other than limestone frag- 

 ments the flat surfaces of which bore no striations. It was thought that 

 the breaking up of the limestone had occurred under the influence of 

 the liquid components of the soil, materially assisted by the mechanical 

 action of the roots of various plants. 



