108 
IOWA ACADEMY OP SCIENCE 
This clay probably resulted from the dolomite by the slow solution of the 
calcium and magnesium carbonates. The typical specimen of the rock referred to 
above contained 0.25 per cent AhOs and 0.34 per cent Fe203; therefore the alumina 
seems to have been removed much more rapidly than the ferric oxide. 
If this deposit resulted from the decomposition of dolomite it must have been 
very slow in forming, and the accumulation of as great a quantity as 13 feet 
must have required a very long time. 
Our thanks are due Mr. Merle S. West for assistance in this investigation. 
