Table 564. 



GEOCHEMICAL DATA. 



423 



Eighty-three chemical elements (86 including Po, Ac and UrXj) are found on the earth. Besides the eight occur- 

 ring uiiconibined as gases, 23 may be found native, Sb, As, Bi, C, Cu, Au, Ir, Fe, Pb?, Hg, Ni, Os, Pd, Pt, Rh, Ru, 

 Se, Ag, S, Ta ?, Te, Sn ?, Zn .''. Combined the elements form about 1000 known mineral species. Rocks are in general 

 aggregates of these species. Some few (e. g., quartzite, limestone, etc.) consist of one specie. We have some knowl- 

 edge of the earth to a depth of 10 miles. This portion may be divided into three parts : the innermost of crystalline or 

 plutonic rocks, the middle, of sedimentary or fragmentary rocks, the outer of clays, gravels, etc. 93% of it is solid mat- 

 ter, 7% liquid, and the atmosphere amounts by weight to 0.0,-1% of it. Besides the g major constituents of igneous rock 

 (see 7th col. of table) 3 are notable by their almost universal occurrence, Ti02, P2O6, and MnO. Bo, Gl, and Sc are also 

 widely distributed. 



Tlie density of the earth as a whole is 5.52 (Burgess); continental surface, 2.67 and outer 10 miles of crust, 2.40 

 (Harkness). Computed from average chemical composition: outer ten miles as a whole, 2.77; northern continents 

 2.73 ; southern, 2.76 ; Atlantic basin, 2.83 ; Pacific basin, 2.88. 



Data of Geochemistry, Clarke, Bui. 616, U. S. Geological Survey, 1916 ; Washington, J. Franklin. Inst. 190, 

 P- 7S7, I920- 



Average Composition of Known Terrestrial Matter. 



Average Composition of Meteorites: The following figures give in succession the element, atomic number 

 (bracketed), and the percentage amount in stony meteorites (Merrill, Mem. Nat. Acad. Sc. 14, p. 28, 1916). The 

 "iron" meteorites contain a much larger percentage of iron and nickel, but there is a tendency to believe that with 

 such meteorites the composition is altered by the volatilization or burning up of the other material in passing through 

 the air. Note the greater abundance of elements of even atomic number (97.2 per cent). 



Smithsonian TABLTiS 



