322 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
constituent of most basic igneous rocks. If iron were a high-priced 
metal, such as tin or copper, of which ores containing 1 or 3 per cent 
are profitably worked, then basalt would be an ore of igneous origin. 
Under present commercial conditions, however, basalt can not be 
regarded as an iron ore. But if the magnetite in a basic rock had 
been segregated into clots or masses large enough and pure enough to 
pay for mining, then they would be iron ores formed by igneous 
action. ‘There are cases of such segregations large enough to be 
mined. The most famous is Taberg, a mountain in Smaland, near 
the southern end of Lake Wetter, in Sweden. It is a locality of 
historic interest; a view of it, as a mountain of iron, was published 
by Peter Ascanius in the Philosophical Transactions“ in 1755, and 
Sefstrém discovered the element vanadium in its ore in 1830. 
Taberg consists of an intrusive mass of rock composed of magnetite, 
olivine, labradorite, and pyroxene. Many theories of its formation 
have been advanced. The view generally adopted is that of 
Tornebohm, who described the rock as a variety of hyperite in 
which there has been a central segregation of magnetite to such an 
extent that some of it contains 31 per cent of iron. Tornebohm 
claims to have traced a gradual passage from normal hyperite to a 
variety poor in feldspar, then to one without feldspar, and finally to 
a granular intergrowth of magnetite and olivine. This Taberg ore 
was mined and smelted for iron in the eighteenth century, when 
transport was more costly and commercial competition less keen than 
it is to-day. The ore has been worked at intervals as late as 1870; 
and as the hill is estimated to contain 100 million tons of ore above 
the level of the adjacent railway, it is not surprising that efforts are 
being again made to utilize the deposit, in spite of its low grade and 
high percentage of titanium. The Taberg hyperite bas almost 
reached the line which divides magnetite-bearing rocks from useful 
iron ores. Its igneous origin, however, has not been universally 
accepted. The theory has been rejected by so eminent an authority 
as Posepny, 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 insignificant value. The 
microscopic sections of the ore show that it is a granular aggregate 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. 
@Vol. XLIX, pp. 30-34, pl. 1. 
oF, Posepny, “The Genesis of Ore Deposits.’ Trans. Amer. Inst. Min. Eng., 
1893, p. 323. 
