500 TRANSACTIONS OF SECTION C. 
The second theory has been advanced independently by Professor de Launay 
and Dr. Helge Bickstr6m: according to them the porphyrites above and below 
the iron ores are lava flows, and the ore was a superficial formation deposited in 
an interval between the volcanic eruptions, According to de Launay the iron 
was raised to the surface as emanations of iron chloride and iron sulphide; the 
iron was deposited as oxide, and most of it subsequently reduced to magnetite 
during the metamorphism of the district. 
The third theory—that the ores are of direct igneous origin—has been main- 
tained by Lofstrand, Higbom, and Stutzer; according to them the ores are 
segregations of magnetite from the acid igneous rocks in which they oeeur. The 
segregation theory has been opposed, amongst others, by de Launay and Vogt. 
Thus, de Launay maintains that the segregation would have been impossible in 
such fluid lavas as the Kiruna porphyrites, and is improbable, since there is no 
transition between the ore and the barren rock. 
The segregation theory has serious difficulties, and is faced by several obvious 
improbabilities. The ore occurs as a band nearly forty times as long as it is 
broad. It has the aspect, therefore, of a bed or a lode. The ore has not the 
granular, crystalline structure of an igneous rock like the hyperite of Taberg, but 
the aspect of a material deposited from solution or formed metasomatically. It is 
almost free from titanium, the undesirable constituent so abundant in the ores of 
Taberg and Routivaara. 
The igneous theory cannot, however, be lightly dismissed, as it is supported 
by the high authority of Professor Hogbom, and therefore demands careful con- 
sideration. 
It has been advanced in two main forms, the one considering the ore to have 
been deposited at the time when the igneous rocks were consolidating, the other con- 
sidering it was deposited at a later period. According to Professor Hégbom, 
the ore was syngenetic, being a true magmatic segregation from a syenite. But, 
according to Dr. Stutzer (1906), the segregation was later than the consolidation 
of the syenite. He describes the lode as an intrusive banded dyke, of which 
the chief constituents are magnetite and apatite; and the injection of this dyke 
pneumatolytically affected the rocks beside it, producing an intermediate zone, 
impregnated with ore, which he compares to contact deposits,’ 
In spite of the high authority of Professor Hiéghom, I am bound to confess 
that the Kiruna ores do not impress me as of igueous formation. Their bed-like 
form, microscopic structure, and poverty in titanium are features in which tbey 
differ from those admittedly due to direct magmatic segregation. The microscopic 
sections that I have examined suggest that both the magnetite and apatite 
were deposited from solution and later than the consolidation of the underlying 
porphyrite, which the ore in part replaces. An examination of the field evidence 
supports the conclusions of de Launay and Backstrom as to the ore being a bedded 
deposit overlying a lava flow, but enlarged by secondary deposition. 
V. Future Supply of Iron Ores. 
This conclusion is perbaps economically disappointing. The possible existence 
of such vast segregations of iron in the acid igneous rocks has an important 
economic bearing. There is only too good reason to fear that the chief iron ores 
are comparatively limited in depth ; for most of them have been formed by water 
containing oxygen and carbonic acid in solution, which has percolated downward 
from the surface. Ores thus formed are therefore restricted to the comparatively 
‘In a later paper, of which only a short abstract has been issued, Dr. Stutzer, 
however, explains that ‘the intrusion of the ore dyke was at relatively the same time 
as the formation of the syenite, and that the ores were formed by magmatic separa- 
tions im situ, or as peregrinating magmatic separations (magmatic veins and bedded 
streams).’ He adds that ‘ pneumatolysis plays no inconsiderable réle in the formation 
of these veins.’ Dr. Stutzer’s position may be summarised as regarding the ores as 
collected by segregation, but deposited in their present position by eruptive after- 
actions, 
