498 ‘TRANSACTIONS OF SECTION C. 
according to whom the ore occurs in solid veins as well as in grains; and he 
holds that, like other Scandinavian iron ores, it was due to secondary deposition, 
During a visit to the mountain, I failed to see any secondary veins, except of insig- 
nificant value. The microscopic sections of the ore show that it is a granular 
ageregate of olivine, generally with labradorite and pyroxene. Hence I have no 
hesitation in accepting the view of the Swedish geologists and regard Taberg as 
a magmatic segregation. Posepny! has in this case carried his Neptunist theory 
of the genesis of ores too far. 
At Routivaara, in Swedish Lapland, there is a still larger mass of magnetite, 
which is claimed, in accordance with the descriptions of Petersson and Sjogren, 
to be due to segregation from the magma of the surrounding gabbro. This mass 
of magnetite is of colossal size, but it is of no present economic value, owing to its 
high percentage of titanium and its remote position. 
An igneous origin is claimed by Professor Hégbom for some small masses of 
titaniferous magnetite in the island of Aln6, opposite Sundsvall, on the eastern 
coast of Sweden. ‘This case is of interest, as the surrounding rock is not basic: 
it is a nepheline syenite, containing only 2 per cent. of magnetite, which, however, 
has been concentrated in places, until some specimens (according to an analysis 
quoted by Professor Hégbom) contain as much as 64 per cent. of magnetite, 
Y per cent. of ferrous oxide, and 12 per cent. of titanic oxide. 
The Alné magnetites, again, are of no practical value, as they are too low in 
grade and too refractory in nature. I understand that about 500 tons of the 
material have been smelted, but with unprofitable results, and the rest of the 
material quarried has been left on the shore. We may therefore accept the iron- 
bearing masses of Alné and Routivaara, as well as that at Taberg, as due to 
magmatic segregation, without having conceded much as to the igneous forma- 
tion of ores. Tbe process in this case has formed rocks, rich in titaniferous 
magnetite, from which iron could be obtained, but rocks which no ironmaster is at 
present willing to buy as iron ore. Whether a basic igneous rock is to be regarded 
as an iron ore, or as only useful for road metal, depends on cost of treatment, 
The definition of the term ‘ore’ is very elastic, Petrographers speak of the minute 
grains of magnetite or chromite in a rock as its ores; but that is a special use of 
the term ‘ore.’ Usually ore means a material which can be profitably worked as 
a source of metals under existing or practicable industrial conditions.? According to 
this definition, the Swedish deposits of titaniferous magnetite are at present doubt- 
fully within the category of iron ores. 
The famous iron mines of Middle Sweden at Dannemorra, Norrberg, Gran- 
gesberg, and Persberg occur under different geological conditions; they work 
lenticles or bands of ores in metamorphic rocks, of which some are altered sedi- 
ments; and the view has therefore been held by de Launay and Vogt that the 
ores also are altered sediments. 
That ores are formed by igneous segregation of suflicient size and purity to be 
of economic importance is a theory which rests on two chief cases—the nickel ores 
of Sudbury in Canada and the iron ores of Swedish Lapland. 
2. The Sudbury Nickel Ores.—The nickel ores of Sudbury are the most import- 
ant historically. ‘They have been repeatedly claimed as of direct igneous origin 
by Bell (1891), von Foullon (1892), Vogt (1893), Barlow (1903), and by other 
geologists; and this view was advocated before the Association at the Johannesburg 
meeting by Professor Coleman. The theory was stoutly opposed by Posepny in 
1898, and Professcr Beck in 1901 described some of the brecciated ore, and showed 
that its metallic minerals are sharply separated from the barren rock. He held 
that such ore must have been formed, not only after the consolidation of the rock, but 
even after or during its subsequent metamorphism. The views of Posepny and Beck 
seem to have been established by additional microscopic study of the ores by C. W. 
1 F. Posepny, ‘The Genesis of Ore Deposits,’ Zrans. Amer. Inst. Min. Eng., 1893, 
p. 323. 
2 The Oxford Dictionary adopts a still more restricted definition; according to 
it an ore is ‘a native mineral containing a precious or useful metal in such quantity 
and in such chemical combination as to make its extraction profitable.’ 
