362 Lever ett — AYeatliering and Erosion as Time Measures. 



sandstone area. The average amount of removal of drift in 

 Post-Kansan time is estimated to be somewhat more than 

 50 feet, at least it would take more than that amount to bring 

 the valleys up to a level with the tabular divides. This is 

 apparent from the sections of maps here presented, and was 

 carefully worked out in the field in a neighboring county of 

 Iowa by Dr. C. H. Gordon, while connected with the Iowa 



Fig. 5. 



Fig. 5. Part of the Atlanta, Missouri, topographic sheet showing Post- 

 Kansan drainage. Scale, 1 : 86500. Contour interval, 20 feet. 



Geological Survey. To the question whether the streams 

 may have begun their work in depressions somewhat below the 

 level of the tabular divides, it is remarked that the lack of 

 correspondence between the tabular drift divides and the 

 preglacial rock divides, together with the consistent fitting in 

 of each tabular divide with its neighbors to form a plain slop- 

 ing in the direction of drainage, as well as the evidence to be 

 gathered from the lateral drainage, gives a strong presump- 

 tion that the surface was brought up very nearly to a plain of 

 the kind preserved in the tabular remnants. 



