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 which 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 with 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 Iowan drift plain, and is within 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. 
