Age of flic Kansaii Drift Sheet— Hcrshey. 21 
The Kansan ice sheet left the territory of northeastern 
^Missouri as a remarkably even plain sloping gently toward 
the southeast. The pre-Kansan erosion topography was com- 
pletely obscured, the valleys having been filled with drift 
(mainly till) to a hight greater than the rock ridges, so that 
the present drainage lines do not conform to the courses of pre- 
glacial streams. There were apparently no moraines or eskers to 
interrupt the evenness of the plain. Although this original drift 
plain has been mainly destroyed by subsequent sub-aerial 
erosion, by looking across the summits of the main divides its 
outline may be distinctly seen. As in the case of a dissected 
peneplain, in the far distance the valleys disappear from view 
and the country has the appearance of yet remaining undissect- 
ed. It seems impossible to account for the fact that the crests 
of the main ridges of drift all fall into a single plane as the 
accidental result of the deposition of drift. 
Xow, the Kansan plain of northeastern jMissouri has been 
very completely dissected. The drainage basins are long and 
narrow, but the vallevs are dendritic in character and the 
topography typically that of erosion. The main valleys have 
been trenched to a depth of 100 to 150 feet and have broad, 
flat bottoms, one-fourth, one-half or not infrequently an entire 
mile in width. They are joined at frequent intervals by tribu- 
tary valleys, the ridges between which have been reduced much 
below the original plain level. In fact, it is only along a few 
of the main divides, as that followed by the Santa Fe railroad 
between LaPiata and Moberly that the original plain remains 
practicallv undissected for a width of as much as one mile. It 
is the' general degradation of the unland which is the most 
striking feature of post-Kansan erosion. 
Railroads in crossing this area transverse to the main 
streams, as does the Santa Fe between LaPlata and the Des 
Moines river, only reach the level of the original plain at rare 
intervals. For three, five, or in places ten miles, in passing 
from one main divide across a basin to another high ridge, 
they are much below the level of the upland. l'ro])ably one- 
half of the material between the level of the main valley bot- 
toms and the original plain, a vertical interval in some sections 
of' 150 feet, has been removed by erosion. In short, in terms 
of the geomorphologists,the topography may l)c said to be com- 
