12 Transaction x. 



mineral-deposits are genetically connected with the intrusion 

 or eruption of igneous magmas. 



It has been shown by Professor Sandberger and others 

 that igneous rocks contain all the constituents of mineral 

 veins. Professor Vogt, of Christiania, maintains that the 

 belief in a deep-seated inaccessible repository of the heavy 

 metals can no longer be sustained.* Modern geologists, he 

 points out, have abandoned the old conception which sup- 

 posed that the interior of the earth was an enormously com- 

 pressed liquid molten mass of high specific gravity charged 

 with heavy metals. The composition of the molten magmas 

 that have issued at the surface in successive geological ages 

 does not favour any hypothesis which assumes the existence 

 of a greater proportion of the heavy metals in the barysphere 

 than in the upper crust, or lithosphere. Eeferring to the dis- 

 tribution of the elements in the earth's crust, Vogt states 

 that of the entire earth-crust — including the rocks, sea, and 

 atmosphere — oxygen constitutes by weight about one-half, 

 and silicon about one-quarter. f The proportion of the other 

 elements are, he says, as follows : — 



Alumina, iron, calcium, magnesium, Per Cent. 



sodium, and potassium ... 10 to 1 



Hydrogen, titanium, carbon, and 



chlorine ... ... ... 1 to Ol 



Phosphorus, manganese, sulphur, 



barium, fluorine, nitrogen, zirco- 

 nium, and strontium ... ... Ol to 0-01 



Nickel, lithium, vanadium, bromine, 



and perhaps beryllium and boron 001 to - 001 

 Cobalt, argon, iodine, rubidium, tin, 



cerium, yttrium, possibly arsenic 



and others ... ... ... 0001 to 00001 



In igneous magmas deficient in acid-forming constituents 

 the heavy metals will segregate as oxides during the process 

 of cooling, assuming the form of individual crystals, grains, or 

 irregular aggregates in small and great masses. 



The petrographical researches of Vogt and Brogger disclosed 

 in basic dykes a tendency of the heavy minerals to segregate 

 near the borders. The occurrence of massive mineral aggre- 

 gates near their borders is a marked characteristic of perido- 

 tites and serpentines in all parts of the globe. 



The most typical examples of magmatic border segregation 

 are found in peridotite and its serpentinised forms. At pre- 



* Professor J. H. L. Vogt, " Problems in the Origin of Ore-deposits," 

 " Genesis of Ore-deposits," 1901, p. 637. (Published by American Insti- 

 tute of Mining Engineers.) 



t Loc. cit., p. 639. 



