452 _ Notices of Memoirs—Professor J. W. Gregory— 
not to the direct consolidation of material from a molten state, but to 
eruptive after-actions due to the hot solutions and heated gases given 
off from cooling igneous rocks. Igneous rocks probably play a notable 
part in the genesis of most primary ore deposits; for the entrance of 
the hot ore-bearing solutions is rendered possible by the heat of the 
igneous intrusions, as Professor Kemp has well shown in his paper on 
‘‘The Role of Igneous Rocks in the Formation of Metallic Veins.” 
Professor Kemp limits the term ‘igneous’ to materials formed by the 
direct consolidation of molten material ; and this decision seems to me 
to be most convenient. For example, the quartzite that is so often 
found beneath a bed of basalt is due to hot alkaline water from the 
lava cementing the loose grains of sand; the process is an eruptive 
after-action, but it would be unusual to call such a quartzite an 
igneous rock. 
1. Zgneous Ores.—That there are ores which are the products of 
direct igneous origin is now almost universally admitted. The 
mineral magnetite is a most valuable source of iron, and it is 
a constituent of most basic igneous rocks. If iron were a high-priced 
metal, such as tin or copper, of which ores containing one or three 
per cent. are profitably worked, then basalt would be an ore of igneous 
origin. Under present commercial conditions, however, basalt cannot 
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 
Sefstrom discovered the element vanadium in its ore in 1880. 
Taberg consists of an intrusive mass of rock composed of magnetite, 
olivine, labradorite, and pyroxene. Many theories of its formation 
have been advanced. he 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 felspar, then to one without felspar, 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 utilise the deposit, in spite of its low grade and 
high percentage of titanium. The Taberg hyperite has 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, 
1 Vol. xlix, pp, 30-34, pl. ii. 
