PRESIDENTIAL ADDRESS. 497 
equal thoroughness by the Neptunists, who refused to concede that volcanic 
action was due to deep-seated cosmic causes. Thus Jameson in 1807 stoutly 
maintained that volcanoes were superficial phenomena due to the combustion 
of beds of coal beneath fusible rocks, such as basalt, and that the explosions were 
due to the sudden expansion of sea-water into steam by contact with the burning 
coal. Volcanoes, according to this view, were correctly described as burning 
mountains, giving forth fire, flame, and smoke. The extreme Neptunist and 
Plutonist schools have long since been extinct, but the controversy is not quite 
closed. The battlefield is now practically restricted to economic geology, and the 
issue is the origin of some important ores. 
Ore deposits present so many perplexing features that deep-seated igneous 
agencies were naturally invoked to explain them, and some of the most thorough- 
going champions of the igneous origin of ores make claims that remind us of 
the eighteenth-century Plutonists. The question is to some extent a matter of 
terms. Many of the ores which Vogt, for example, describes as of igneous origin 
he attributes, 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 o! the hot ore-bearing solu- 
tions 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. JT’or 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. Igneous 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 isa locality of historic interest ; a 
view of it, as a mountain of iron, was published by Peter Ascanius ' in the ‘ Philo- 
sophical Transactions’ in 1755, and the element vanadium was first discovered in 
its ore by Sefstrém 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 Térnebohm, 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, Térnebohm 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 rock 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. 
1907. K K 
