3l6 TRANS. ST. LOUIS ACAD. SCIENCE. 



lost in a measure along slopes where the natural drainage is su- 

 perior and the subsoil is leached to a considerable depth by more 

 freely percolating waters. It is unquestionably to this peculiarity 

 of the soil that the confinement of forests to slopes and valleys 

 is due ; and the superior porosity and fertility of the naturally 

 drained soils indicates that the "sour" soils of the plains might 

 be gradually reclaimed by means of persistent and thorough 

 imder-drainage. 



It should be added that the peculiar phase of the drift rep. 

 resented in the upper portions of the Alacon county sections 

 may be observed throughout nearly the whole of the area 

 of fifty thousand square miles or more characterized by the 

 peculiar topography already described, though it is frequently 

 overlaid by loess or other superimposed deposits ; and it seems 

 probable that the upper portion of the drift throughout this whole 

 region was laid down in a continuous body of water by whose 

 M^aves the great plains were fashioned, and that the characteristic 

 autogenetic drainage of these plains was developed as the waters 

 receded. 



TJie Relations of the Deposits. — Neither glacial drift nor allu- 

 vium were traced southward beyond the limits of Macon county, 

 nor were they directly correlated with the "second bottom," the 

 Port Hudson, the loess, or other deposits of central and south- 

 eastern Missouri. But the former was traced northward into a 

 region already carefully studied in southern Iowa, in which the 

 superior phase maintains its characters and has received various 

 local designations commonly expressive of its character as a soil 

 — "gumbo," "hard-pan," "white clay," " push-land," " crawfish 

 flats," etc., — and in which, as in Missouri, the upper portion gra- 

 duates imperceptibly downward into unmodified glacial drift.* 

 Here, however, the drift is frequently overlaid by loess, a forest 

 bed being sometimes intercalated, and somewhat farther north- 

 ward another drift-sheet comes in at the base of the loess and 

 above the forest bed ; and the loess frequently graduates imper- 

 ceptibly downward into the newer drift, much as the laminated 

 portion of the Macon county drift sheet graduates into its lower 

 portion. The full sequence of deposits is therefore : 



* Trans. Iowa State Hort. Soc. for iSSi, vol. i6, 227 40. 



