THE ORIGIN OF GUMBOTIL loi 



Feet Inches 



6. Gumbotil (Illinoian), gray to ashen-color on 

 dry surface; on fresh surface, gray mottled 

 with brown; small pebbles; leached; grades 

 into No. 5 4 6 



5. Glacial till (Illinoian), oxidized brownish, 



contains bowlders, leached 5 6 



4. Glacial till (lUinoian), oxidized, unleached, 

 has concretions, breaks into irregular shaped 

 fragments i 



3. Gumbotil (Kansan), drab to dark color, 

 starchlike fracture, some calcareous concre- 

 tions; few pebbles; leached; grades into No. 2 8 6 



2. Glacial till (Kansan), oxidized, pebbles and 

 bowlders, leached 5 



I. Glacial tUl (Kansan), oxidized, unleached, 

 many concretions, breaks with irregular frac- 

 ture, exposed 12 



The transition zone between gumbotil and the base of the oxidized 

 leached drift. — Many interesting sections might be given to show 

 disintegrated and decomposed bowlders in the transition zone 

 between gumbotil and the base of underlying leached and oxidized 

 till. For example, on the east-west wagon road in section i. 

 Otter Creek Township^ Lucas County, Iowa, there is in the transi- 

 tion zone between the Kansan gumbotil and the base of the leached, 

 oxidized Kansan till a granite bowlder with dimensions of 4 X 2 feet 

 on the slope. It is so thoroughly weathered that its outlines are 

 discerned only with difficulty. Again, in a cut through the upland 

 \ mile north of Forbush on the interurban railway between Center- 

 ville and Moravia, Appanoose County, Iowa, there is in the transi- 

 tion zone between Kansan gumbotil and the base of the oxidized, 

 leached Kansan till a completely disintegrated granite bowlder 

 5 feet long by 2 feet wide as exposed on the surface. 



The pebble content of gumbotil and underlying drift. — The gumbo- 

 tils and underlying tills were studied also with regard to their 

 pebble content to ascertain whether or not additional evidence 

 could be obtained to strengthen the view that the gumbotils 

 are the result of changes in what was originally till. 



