Pi'ohleiiit< of Me ml) l Iron Ore. — Wivchell. 173 
be celebrated. This has recently been discovered in indefinite 
and almost incalculable amounts. It is generallj' amorphous, but 
in lumps, frequently as if a breccia of some sedimentary' rock, 
easily crushed, and it also exists as a granular powder, finer than 
mustard seed, and can be mined by the simplest methods. The 
plans now being entered upon for excavating it only require a 
steam shovel and a railroad train. 
Stratigraphic relations. 
The horizon in which this ore occurs is that which has been 
identified as Taconic, or primordial. The strata have a gentle 
dip toward lake Superior, and a uniform strike from one end of 
the range to the other. The strata are as follows in descending 
order, omitting minor variations. 
1. Black slate with interbedded sheets of eruptive materials 
which are widespread and non-amygdaloidal. 
2. Gabbro out-break. Titanic ore horizon. The line of this 
outbreak is found not to follow the present northern strike of the 
hematite ore horizon, but to encroach upon it, giving hard ores in 
the eastern end of the range, while toward the west its line of 
outbreak turns more southerl}', passing the head of lake Superior 
at Duluth, but apparently forming a bed of conglomerate and 
breccia along the ore belt, noted at various places between Grun- 
flint lake and Pokegama falls. 
3. A peculiar siliceous rock, partly jasperoidal, partly of hard 
hematite, or hard limonite, sometimes conglomeritic and brec- 
ciated, chert}', flinty, usually gray, sometimes parti}' black or 
purple, and, toward the west, kaolinic, toward the east holding 
some magnetite. Altogether this is a non-descript rock, which 
sometimes is fifty feet in thickness, but so far as developed near 
the mines is less than twenty. It is a pretty constant rock and 
when the ore is absent it lies on or varies to the Pewabic quartzj'te. 
This is the horizon of the hard hematite, hard limonite and of 
some of the non-titanic magnetite. In some way not yet fully 
determined it is associated with the next. It is not yet certain 
that all the soft ore is derived from a change of this rock to ore, 
but it is very certain that in some cases this rock is converted to 
ore. It overlies, apparently, the chief ore body of the range, or 
its lower portion is changed to ore. 
4. The chief horizon of soft hematite. The greatest thickness 
this bed has yet been found to exhibit is 105 feet. In the midst 
