68 



SOILS: PROPERTIES AND MANAGEMENT 



ANALYSES OF RESIDUAL AND GLACIAL CLAYS FROM THE DRIFT- 

 LESS AND GLACIATED AREAS OF WISCONSIN 



These analyses illustrate to very good advantage the 

 beliefs entertained by Chamberlain and Salisbury regard- 

 ing the differences between residual and glacial clays. 

 Residual clay is designated by them as " rock rot/' and 

 glacial clay as " rock flour." The latter, being less 

 weathered, retains a larger proportion of its easily soluble 

 materials. It is to be noted here, as in the comparison 

 of marine and residual soils, that silica, aluminium, and 

 iron are lower in the soil subjected to the less amount of 

 leaching, which in this case is the glacial clay. This in 

 itself would serve to indicate that the important plant- 

 food constituents are generally present in larger quanti- 

 ties in the glacial clay. In fact, it would be expected 

 that the glacial soils would approximate very closely the 

 rock or rocks from which they came. The phosphoric 

 acid, lime, sodium, magnesium, and potash of the residual 

 soils in this case amount on the average to 5.73 per cent, 

 while that of the glacial clays reaches the high figure of 

 24.61 per cent. This is due largely to the great amount 



