GEOLOGY OF THE INNER EARTH—GREGORY. 323 
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 Alné, 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, con- 
taining only 2 per cent of magnetite, which, however, has been con- 
centrated in places, until some specimens (according to an analysis 
quoted by Professor Hogbom) contain as much as 64 per cent of 
magnetite, 9 per cent of ferrous oxide, and 12 per cent of titanic oxide. 
The Alno 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 unprofit- 
able results, and the rest of the material quarried has been left on the 
shore. Wemay 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 formation of ores. 
The 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 doubtfully within 
the category of iron ores. 
The famous iron mines of middle Sweden at Dannemorra, Norr- 
berg, Gringesberg, and Persberg occur under different geological 
conditions; they work lenticles or bands of ores in metamorphic rocks, 
of which some are altered sediments; 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 sufficient size and 
purity to be of economic importance is a theory which rests on two 
b 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.” 
