278 IOWA. ACADEMY OF SCIENCES. 



First. Buried soil. Lying between two thick beds of 

 drift there is an apparent soil horizon, dark brown in color, 

 in w^hich are imbedded numerous small bits of wood and 

 darker colored fragments of organic matter. 



Second. Leaching. The bed of clay which overlies the 

 soil horizon is very calcareous to the base. The soil band 

 contains no trace of calcareous matter, nor does any such 

 material appear for a depth of two feet below it. At a depth 

 of thirty inches a slight quantity is present in the clay. This 

 quantity gradually increases with the depth until at six feet 

 below the soil band and from there to the base of the ex- 

 posure the quantity is considerable as shown by the vigorous 

 action wdth acid. This would indicate a long interval dur- 

 ing which the old soil band was at the surface and subjected 

 to the leaching effects of the atmosphere and of percolating 

 water before it was buried by the overlying materials which 

 were carried by a later sheet of ice. 



Third. Oxidized zone. The reddish color of the clay to 

 a depth of three or four feet below the soil horizon would 

 indicate a period during which these materials were exposed 

 to the oxidizing effects of the air. The oxidation resulted 

 in the changing of the iron found in the clay from the form 

 of carbonate, in which form it usually occurs in the blue 

 clays, to that of the oxide known as hematite, in which 

 form it imparts a reddish color to the clays when it is 

 present; 



The above exposure is about eight miles south of the 

 border of the lowan drift plain, and is wdthin the area in 

 which the Kansan drift forms the surface materials. It is 

 thought by the writer, that Number 3 of the exposure 

 represents the Kansan drift; Number 2, the soil horizon 

 which represents the Aftonean interglacial period, while 

 Number 1 is referred to the bowlder clay of the pre-Kan- 

 san drift sheet with its upper portion leached and partially 

 oxidized as described above. 



