360 Leverett — Weathering and Erosion as Time Measures. 



the Illinoian, is not seen in the Riss and the Middle Diluvium, 

 nor is there the deep penetration of weathered pipes and seams 

 into the unweathered portion. The Kiss moraines have not 

 the sharp hummocks that characterize the Wiirm moraines, but 

 the contrast is not much more striking than is found between 

 our Earlier and Later Wisconsin moraines. The impression one 

 obtains is that the Riss and the Middle Diluvium have reached 

 a condition of weathering intermediate between our Earlier 

 Wisconsin and our Illinoian drifts. Further study into cli- 

 matic conditions in the several fields and into the constitution 

 of the drift deposits may serve to remove some of the difficulties 

 of correlation. Portions of the area of the Middle Diluvium 

 lying east of the Harz Mountains have at present a very light 

 rainfall, which seems to produce less leaching than is accom- 

 plished in more humid districts to the west. Possibly long 

 continued aridity will account for the lack of deep penetration 

 of weathered pipes and seams. At present waters charged 

 with calcareous constituents rise into the soil by capillary 

 action and tend to keep it well supplied with calcareous mate- 

 rial. Prof. Keilhack reports that the calcareous material is in 

 the form of a coating on the grains of silica, feldspar, etc., and 

 not in the form of grains or coarse particles of limestone. In 

 other words, the present calcareous content is secondary. 



So far as inferences can be drawn from relative amounts of 

 erosion these European drifts differ but little from the Illi- 

 noian in the places where erosion conditions are similar as to 

 gradient and texture of deposit. The erosion of the high ter- 

 races (Hochterrassen), which connect with the Riss moraines 

 of the Alpine region, seems to be about as great as the ordi- 

 nary erosion of the Illinoian drift under good stream gradients. 

 The erosion of the Middle Diluvium has been sufficient to 

 remove nearly all traces of the deposit along the borders of 

 the main drainage lines, which compares favorably with the 

 amount of erosion in our Illinoian drift. 



Kansan Drift. 



The Kansan drift, which is the most extensive sheet of 

 the Keewatin field, is widely exposed in northern Missouri, 

 southern and western Iowa, and neighboring parts of Kansas 

 and Nebraska. Its northern portion is concealed by the Wis- 

 consin drift. The greater part of this drift, like the Illinoian, 

 is covered by loess. Some of this deposit may be older than 

 the Illinoian drift, at least loess has been found between the 

 Kansan and the Illinoian in the district along the Mississippi 

 where the Illinoian overlaps the Kansan drift. A large part 

 of the loess, however, seems to be of the same age as that which 



