42 IOWA ACADEMY OF SCIENCES. 



The sample above this as follows: 



SiOj 67.85 



AljOg+FeaOa 2045 



CaO 1.19 



Mn O trace 



Ka O- trace 



Loss dried at 100°... 3.47 



Loss by ignition 7.12 



Total.. 100.08 



It will be seen that in each there is a large per cent, of silica 

 and alumina. The upper containing more free silica, conse-* 

 quently gave a higher per cent of silica and alumina, but con- 

 tained a considerably smaller per cent, of hygroscopic moisture, 

 The higher loss by ignition in the upper stratum being due 

 doubtless, to a larger amount of organic matter near the sur- 

 face. Lime was present in the upper stratum in appreciable 

 quantity, and iron in small quantity in each. A trace of man- 

 ganese oxide in the upper stratum. 



From Crossley's "Table of Analyses of Clays" for common 

 brick we take three average samples, which are as follows: 



Common brick clay: 



SiOj 49.44 



Alj O3 34.26 



Pe^ O3 7.74 



CaO 1.48 



Mg O 5.14 



Water and loss 1.94 



Total 100.00 



Sandy clay: 



Si Oj 66.68 



Alj O3 26.08 



Fej O3 1.26 



Mg O trace 



CaO 84 



Water and loss 5.14 



Total 100.00 



Marl. — London "Malms." 



Si02+Al2 03 43.00 



Fe^ O3 3.00 



CaO 46.50 



Mg O 3.50 



Water. 4.00 



Total 100.00 



