EARTH'S CEUST WASHINGTON. 287 



posedly rare elements are widely distributed, notably barium, stron- 

 tium, chromium, vanadium, nickel, and even molybdenum. 15 



In Table II it is also noteworthy that, of the metals in daily and 

 common use, only aluminum, iron, manganese, chromium, vanadium, 

 and nickel appear among those elements that are present in the rocks 

 of the crust in sufficient amount to be commonly determinable by the 

 usual processes of analysis. Such common and " every-day " metals 

 as copper, zinc, lead, tin, mercury, silver, gold, platinum, anti- 

 mony, arsenic, and bismuth — metals that are of the utmost importance 

 to our civilization and our daily needs — all these are to be found in 

 igneous rocks, if at all, only in scarcely detectable amounts. Though 

 they are ultimately derived from the igneous rocks, they are made 

 available for our use only by processes of concentration into so-called 

 ore bodies. 



To give some concrete and striking figures, it may be pointed out 

 that the eight most abundant elements of the earth's crust (oxygen, 

 silicon, aluminum, iron, calcium, sodium, potassium, and mag- 

 nesium) — the only ones whose amounts are over 1 per cent — constitute 

 together 98.63 per cent of the crust. These, with titanium, phos- 

 phorus, hydrogen, and manganese — 12 in all — make up 99.612 per 

 cent ; thus leaving but about 0.39 per cent for all the other elements, 

 among them some that are quite indispensable for our existing civili- 

 zation. 



A cursory examination shows that the most abundant elements in 

 the earth's crust are, on the whole, those of low atomic weight, as has 

 been often pointed out, while the rarer ones are, in general, those of 

 higher atomic weight. It has also been pointed out by Clarke 16 that, 

 considering the several elements of any group in the periodic table 

 (for which see p. 289), while the first member is comparatively rare, 

 the second is the most abundant (the oxygen group being the only ex- 

 ception), and the members become increasingly rare with increasing 

 atomic weight. This is well seen, for example, in group 1 (lithium, 

 sodium, potassium, rubidium, and caesium) ; in group 2 (glucinum, 

 magnesium, calcium, strontium, and barium), though here we have 

 inversions of the rule in the relative abundance of magnesium and 

 calcium, and of strontium and barium. It is also seen in the third 

 group (boron, aluminum, scandium, gallium, etc.) ; in the fourth group 

 (carbon, silicon, titanium, zirconium, and cerium) ; in the fifth (nitro- 

 gen, phosphorus, arsenic, and antimony) ; in the sixth (oxygen, sul- 

 phur, selenium, and tellurium) , here again there being an inversion as 

 regards the first and second; and in the seventh (fluorine, chlorine, 



16 Cf. Hillebrand, Jour. Amer. Chem. Soc, xvi, pp. 81-93, 1894 ; Amer. Jour. Sci., vi, p. 

 209, 1898 ; U. S. Geol. Survey, Bull. 700, p. 24, 1919. 



16 Clarke, F. W., Data of Geochemistry, U. S. Geol. Survey, Bull. 695, p. 39, 1920. 



