THE ORIGIN OF GUMBOTIL 95 



till, oxidized yellowish for several feet vertically, below which is the 

 normal, unoxidized and unleached, dark grayish to bluish-black 

 Kansan till. An impressive feature of the unleached, oxidized 

 till is the presence of numerous concretions of calcium carbonate, 

 the lime of the concretions having been dissolved in connection 

 with the formation of the overlying gumbotil and leached till, carried 

 downward and later precipitated. 



Some sections showing the relations of Kansan gumbotil to under- 

 lying Kansan drift. — The following sections are given as typical 

 of many sections that have been studied at widely separated places 

 in the Kansan-drift areas of Iowa. They are intended to show 

 the intimate field relations of the Kansan gumbotil to the under- * 

 lying till. 



Section in cut on the Chicago, Milwaukee & St. Paul Railway 

 about one mile east of Foster Station, in the southeast corner of 

 Monroe County, Iowa: 



Feet Inches 



5. Soil, black, porous 2 



4. Loesslike clay, chocolate-colored, leached .... i 6 



3. Loesslike clay, light-colored, grayish; on dry 

 surface looks like gumbotil; has chocolate- 

 colored stains; sticky when wet; contains a 



few small siliceous pebbles; leached 5 6 



2. Gumbotil (Kansan), gray-colored, in lower 

 part chocolate-colored; few pebbles; starch- 

 like fracture when wet ; leached 12 



I. Glacial till (Kansan), brown color, with very 

 irregular patches of gray-colored till resem- 

 bUng gumbotil; dry surface of the till is 

 brownish yellow; damp surface is chocolate- 

 colored; few pebbles; leached to base of cut 5 



Section in cut on the Chicago, Burlington & Quincy Railway 

 at mile 372, one mile west of Murray Station, Clarke County, Iowa: 



Feet 



4. Loesslike clay, gray to pale-yeUowish color, 

 with irregular lines of brown on dry surface; 

 when damp it is grayish with mottling of 

 yeUow to brown colors; stands vertically, 

 upper few feet mealy 15 



