ORES OF IRON 139 
igneous rocks of the Keweenawan. All the rocks are pre- 
Paleozoic, as the Keweenawan is correlated with the 
Scottish Torridon Sandstone. The ore is generally hematite, 
and contains usually between -02 and -05 per cent. of phos- 
phorus ; it occurs in very varied positions, which have one 
feature in common. The ore-bodies rest on an impermeable 
Fig, 42.—LakE Superior IRoN Ores. - 
The Mesabi type (after H. Garde, Bik. ¥ern-Kontorets Ann., 1918). The 
ore occurs as a widespread sheet beneath an old land surface, and 
overlies and is partly interbedded with iron-bearing chert, 
lL Quartzsite, 
Old land surface. 
Iron ore. 
Iron-bearing chert (taconite). 
bed which may be a synclinal in slate or serpentine, or it 
may, as at Mesabi, fade off in irregular tongues into ferrugin- 
ous or greenalite chert. The iron ore has been formed 
by replacement and deposited where solutions, which had 
dissolved iron from the overlying red sandstones of the 
Keweenawan or from basic igneous rocks, or from ferru- 
ginous or greenalite cherts, were stopped in their descent 
(Fig. 43). The bulk of the iron probably came from an oolitic 
Fra. 43.—Lake Superior ORES. 
The Lake Superior ores formed by replace- 
ment bounded below by an impermeable 
surface. From Cuyuna, Minnesota, 
(after Van Barneveld). The rocks con- 
sist of cherty iron carbonates, amphi- 
bolite, slate, diabase dyke, DD. The 
ore is in solid black. 
) 
chert series in which the ore was a chemical precipitate as in 
the Mesozoic and Clinton bedded ores. 
The Gellivaara and Adirondacks—The famous ore-field of 
Gellivaara in Swedish Lapland contains massive bodies of 
magnetite in biotite-gneiss. - The Ifoot-wall of the chief 
body at Gellivaara that was being worked at my visit was