Problems of Memhi Iron Ore. — ^VineheII. 177 
that it is the result of some grand substitution process b}' which 
hematite has been made to take the place of the original sedi- 
ments. There are besides numerous minor evidences of some 
transition in the rocli from its original composition to hematite, viz. : 
(a) Sometimes a gradual encroachment of a hematitic colora- 
tion from the outer portions of a block, or layer, upon a gray or 
blue central area. 
(b) Sudden cessation of a band of hematitic coloration at a 
fissure which evidently the waters producing the coloration could 
not pass, and the passage of the same waters, as shown by the 
narrow streak of hematite in the fissure, down the fissure away 
from the band before affected, leaving that portion on the 
other side of the fissure unstained — while at the same time the 
sedimentary banding of the whole rock sweeps unimpaired across 
the whole face, from one side of the fissure to the other. 
(c) There are larger areas where, as revealed by some of the 
shallow shafts on the western end of the Mesabi range, there is 
an abrupt change, horizontally, from rock to ore, the separating 
line being distinct for a perpendicular distance of at least two 
feet. In other places in the same shaft the ore and rock encroach 
irregularly upon each other. In these cases the ore is soft red 
hematite. If the process of substitution were now going on it 
would be reasonable to expect the oxide would be hydrated, es- 
pecially as such transition is within a few feet of the surface and 
easily accessible by atmospheric waters. 
(d) Not only is the rock changed in situ, but as breccias and 
gravels large deposits are found in which the pebbles, rounded as 
in a river current, or on an ocean beach, are converted to hema- 
tite. Such pebbles were rounded while still rock, and were sub- 
sequently converted to hematite. This is evinced by the varying 
texture, and concentric structure which change somewhat regu- 
larly from the surface to the centre, the outer crust being dense 
and the central portions being vesicular. Whether such pebbles 
appertain to the rocky strata, or are of the age of the drift, has 
not as yet been determined. 
Some necessary jyostufates. 
Notwithstanding it seems inadmissable to adopt any theory 
proposed thitherto for the origin of this ore, and that we ai"e not 
qualified to propose a new oi;e, there are some important facts 
