Leverett — Weathering and Erosion as Time Measures. 363 



The Kansan drift, in places where erosion has been at a 

 minimum, as on the tabular divides, has a weathering to a 

 depth of several meters. There is more or less complete 

 removal of limestone pebbles as well as of finer calcareous 

 material to an average depth of 1-J to 2 meters. Apparently 

 the deposit originally was as calcareous at its surface as in its 

 unleached portion. It lies in a region where limestone forma- 

 tions have extensive outcrops and there are numerous calcareous 



Fig. 6. 



Fig. 6. Part of Edina, Missouri, topographic sheet showing Post-Kansan 

 erosion. Scale, 1 : 173000. Contour interval, 20 feet. The map on this 

 scale is introduced for purposes af comparison with that of the so-called 

 Iowan, fig. 7, which has the same scale. 



nodules at the base of the leached part testifying to a contribu- 

 tion of lime from it. The uppermost half meter of the leached 

 portion is often of a decidedly red tinge, below which is a 

 transition through brown to yellow and finally to gray or blue 

 in a space of 4 to 6 meters or more. The statements just made 

 represent conditions in the humid Mississippi valley where 

 there is an average rainfall of about 40 inches. But as one 

 passes westward into the semi-arid districts along and west of 

 the Missouri River, the amount of leaching in this drift sheet 

 is found to become markedly less, and that too where erosion 

 has been fully as great as in the Mississippi valley. 



