EARTH 'S CRUST WASHINGTON". 



Table I. — Average composition of the earth's crust. 



Silicon dioxide (Si0 2 ) 



Aluminum sesquioxide (AI0O3) 



Ferric oxide (Fe 2 O s ) 



Ferrous oxide (FeO) 



Magnesium oxide (MgO) 



Calcium oxide (CaO) 



Sodium oxide (Na20) 



Potassium oxide (KjO) 



Water (H 2 0) 



Titanium dioxide (Ti0 2 ) 



Phosphorus pentoxide (P : 0&) . 



Manganous oxide (MnO) 



Carbon dioxide (C0 2 ) 



Zirconium dioxide (Zr0 2 ) 



Sulphur(S) 



Chlorine(Cl) 



Fluorine(F) 



Chromium sesquioxide (CroOn) 

 Vanadium sesquioxide (V 2 3 ). 



Nickelous oxide (NiO) 



Barium oxide (BaO) 



Strontium o"xide (SrO) 



Lithium oxide (Li 2 0) 



283 



59.83 

 15.02 

 2.62 

 3.43 

 3.74 

 4.83 

 3.37 

 3.05 

 1.90 

 .79 

 .29 

 .10 

 .49 

 .023 

 .10 

 .063 

 .10 

 .048 

 .026 

 .026 

 .10 

 .043 

 .011 



100.000 



1. Latest estimate, Clarke and Washington, 1920. 



2. F. W. Clarke (first estimate). Bull. Phil. Soc., Wash., xi, p. 135, 1889. 



3. Washington. U. S. Geol. Survey, Prof. Paper No. 99, p. 108, 1903. 



4. Clarke, U. S. Geol. Survey Bull., No. 695, p. 28, 1920. 



Iii Table I there is given the most recent calculation of the average 

 igneous rock, together with three of the most important of the 

 earlier estimates. As regards No. 1, it is to be noted that the figures 

 for the main constituents, from silica to water, inclusive, were 

 arrived at by dividing the sums total of the various determinations 

 by the whole number of analyses, as all of these constituents were de- 

 termined in all the analyses used. For the minor constituents, from 

 titanium dioxide to lithium oxide, inclusive, the figures given are 

 the means of the sums total of the various constituents divided by the 

 whole number of analyses and also by the number of determinations. 

 The former would presumably give a minimum and too low an 

 average and the latter would probably be too high, while the mean 

 would be probably rather nearer the true figure. This matter has been 

 discussed by Clarke and b}^ me elsewhere, and w T ill be enlarged on 

 further in our joint publication. The figures given here should be 

 considered as provisional, as adequate discussion of their relative 

 merits is not called for here. The figure for fluorine is almost -cer- 

 tainly too high, as are probably those for chromium, barium, and one 

 or two other oxides, while possibly that for carbon dioxide is a 

 trifle too low. 



From No. 1 it will be seen (and the same is approximately true 

 of all the others) that the first nine oxides (from silica to water, 

 inclusive) constitute 98 per cent of the whole, and that these, with 

 the oxides of titanium, phosphorus, and manganese, make up to- 



