CLARKE AND STEIGERI META.LLIC ELEMENTS 59 



pies, collected by E. W. Shaw. For the determination of NiO, 

 CiiO, PbO, ZnO and AS2O5, 200 grams of the silt were taken. The 

 presence of organic matter prevented the separate, determina- 

 tion of ferrous iron. The chlorine in this analysis is doubtless 

 due to salt from the Gulf of Mexico. 



TABLE 1 

 Composite Analysis of 235 Samples of Mississippi Silt 



SiO, 69.96 CI 0.50 



AI263 10.52 F 0.07 



FeoOs 3.47 CroOs 0.01 



MgO 1.41 V2O3 0.02 



CaO 2.17 NiO 0.017 



NasO 1.51 MnO 0.06 



KoO 2.30 BaO 0.08 



H2O- 3.78 SrO trace 



H2O+ 1.96 CuO 0.0043 



TiOo 0.54 ZnO 0.0010 



ZrO, 0.05 AsiOs 0.0004 



CO2 1.40 PbO 0.0002 



P2O5 0.18 Organic 0.66 



SO, 0.03 100.6229 



S 0.07 Less 0.13 



100.4929 



For the four composite analyses aboye mentioned the data 

 under immediate consideration are as follows : 



A. The ''red clay" of the oceanic depths. Composite of 51 sam- 

 ples, dredged from the sea bottom and representatiye of all the 

 great oceans. The larger part of this material was collected by 

 the Challenger Expedition. Determinations (by E. C. Sulliyan) 

 of CuO, ZnO, PbO and AsoOs made on 150 gram portions. 



B. "Terrigenous clays," from oceanic depths of 140 to 2120 

 fathoms. Composite of 52 samples, namely 4 ''green muds," 

 and 48 "blue muds," also mainly from the Challenger Expedition. 

 Determinations made on 300 gram portions. 



C. Composite of 235 samples of Mississippi silt, as in the fore- 

 going analysis. For the heax-y metals 200 gram portions were 

 taken. 



