456 Notices of Memoirs—Professor J. W. Gregory— 
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 ora 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 consideration. 
It has been advanced in two main forms, the one considering the 
ore to have been deposited at the time when the igneous rocks are 
consolidating, the other considering 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 inter- 
mediate zone impregnated with ore, which he compares to contact 
deposits.? 
In spite of the high authority of Professor Hogbom, I am bound to 
confess that the Kiruna ores do not impress me as of igneous 
formation. Their bed-like form, microscopic structure, and poverty 
in titanium are features in which they 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 under- 
lying 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 Lron Ores.—This conclusion is perhaps 
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 limited 
depths to which water can carry down these gases. On the theory, 
however, that these ores are primary segregations from deep-seated 
igneous rocks there need be no limit to their depth. They would 
' 1 Tn 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 — 
separations in situ, or as peregrinating magmatic separations (magmatic veins and 
bedded streams).’’ He adds that ‘‘ pneumatolysis plays no inc_nsiderable 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. ae 
