ProhJt'ins of MfxaJjl Iron Ore. — WlncheU. 171 
schistn. or otiirr mrk. When rocks deca}', it makes but little 
(lift'erence what the}' are. the}' part with their contained iron. 
It may go otT in solution, if the proper acids lie present, and ])e 
gathered as oxide under ordinary natural drainage and weather- 
ing, in considerable quantities, on the evaporation of the solvent at 
some lower level. This process has been suggested as the possi1)le 
cause of the accumulation of these ores at the stratigraphic hori- 
zon where they occur. 
4. Accumulation in fnniyhs fonncd hy d ijL-cs cuftiitg tUtcd -if rata 
at a somrwhat uniform inclinatii>n. the iron itself being supposed 
to have been carried down and deposited by ferriferous waters, 
replacing a supposed -'cherty carbonate. "' This hypothesis in- 
volves the same conditions and processes as No. 1 above, but also 
gives explanation of the location of the supposed ore lenses. At 
the same time it involves the decay and concentration in a definite 
rock horizon which is demanded by No. 3. 
5. Deposition from oceanic solution at the time of the 
formation of the rocks associated. That the iron ores of the 
Keewatin age were deposited from solution, has been inferred from 
their association with rocks whose composition requires the 
cotemporaneous action of eruptive forces — bat which are strati- 
fied by oceanic agency — such eruptive action causing chemical re- 
actions that would result in the precipitation of iron and silica. 
This hypothesis has been applied by the writer also to a portion 
of the Mesabi ores, viz. , such as are embraced as somewhat ir- 
regular (wandering) strata in the lower portion of the formation. 
8uch may be either hematite or magnetite. It may perhaps be 
extended farther than has been proposed. 
Some ftcts of the manner of occurrence. 
The Mesabi iron range extends, within the limits of Minnesota, 
a known distance of more than 150 miles, and it is iron-bearing 
through its whole extent. It commences at the west end of 
Gunflint lake, on the national boundary, and has been partially 
explored southwestwardly as far as the Mississippi river near the 
falls of Pokegama. The iron horizons do not fluctuate in their 
stratigraphic positions. The iron varies as the character of the 
accompanying rock varies. It is a duplex range and embraces 
ores of two distinct origins and kinds. 
The more southerly portion of the range, which is made up of 
