42 IOWA ACADEMY OF SCIENCES. 



The sample above this as follows: 



SiOj.... 67.85 



Al^Og+FejOg 20 45 



CaO 1.19 



Md O trace 



K2 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: 



Si O2 49.44 



Alj O3... 34.26 



Fcj O3 7.74 



CaO 1.48 



Mg 0-... 5.14 



Water and loss 1.94 



Total 100 00 



Sandy clay: 



Si Oj 66.68 



AI2 O3 26.08 



Fe^ O3 1.26 



Mg O trace 



Ca O 84 



Water and loss 5.14 



Total 100.00 



Marl. — London "Malms."' 



Si02+Al2 03 43.00 



Fej O3- 3.00 



CaO... 46.50 



Mg O 3.50 



Water 4.00 



Total 100.00 



