SCIENTIFIC SUMMARY. 
101 
according to the direction of the stratigraphical system to which the initial 
fracture of the vein is related. 
The Iron Mines of Michigan . — An article on these mines is in a late 
No. of the American “ Polytechnic Bulletin ” (a new journal). It says that 
in Michigan there are five varieties of ore, of which the most valuable 
so far developed is the Specular, which is a very pure sesquioxide, giving a 
red powder, and yielding in the blast-furnace from 60 to 70 per cent, of 
metallic iron. The ore occurs both slaty and granular or massive. It is 
often banded or interlaminated with a bright red quartz or jasper, and is 
then called u mixed ore.” Probably the next in order of importance is the 
soft Hematite, which much resembles the brown Hematite of Pennsylvania. 
This ore is generally found associated with the harder ores, from which 
many suppose it is formed by partial disintegration. It contains some 
water, chemically combined, is porous in structure, yields about 55 per 
cent, of metallic iron in the furnace, is more easily reduced than any other 
ore of the district, and it forms an excellent mixture with the Specular. 
There are probably several varieties of this ore which have not been well 
made out. That found at the Jackson, Lake Superior, and New England 
mines is associated with the Specular, while the Foster bed is several 
miles removed from any known deposit of that ore. The magnetic ore of 
the district has thus far been found only to the west of the other ores. 
At the Washington, Edwards, and Champion mines, no variety but this is 
known to exist except the Specular, into which the Magnetic is thought 
sometimes to pass, the powder passing from black to purple, then red. 
This view is said to be strengthened by the fact that the Specular ore is 
found in octahedral crystals, which form is well known to belong to the 
magnetic oxide ; hence, it is alleged, that the specular deposits were once 
magnetic, which by some metamorphic action have been robbed of one- 
ninth of their oxygen, which would make them chemically anhydrous He- 
matite. The Flag ore is a slaty or schistose silicious Hematite, containing 
rather less iron, and of more difficult reduction than either of the above 
named. It is often magnetic, and sometimes banded with a dull red or 
white quartz. This ore varies much in richness, and comparatively little 
has been shipped. It is probably the most abundant ore in the district. 
A Silicious ore, containing a variable amount of oxide of Manganese, is 
found at several points, accompanying the Flag ore. This ore is unques- 
tionably of great value as a mixture, but as it has just been introduced, its 
importance has not been determined. The generally received geological 
theory of the origin of these ores is, that they were aqueous deposits, 
which have been highly metamorphosed. The masses are lens-shaped, 
varying much in thickness, on which the value of the mass chiefly depends. 
These masses are interstratified with a soft green slate, which always 
accompanies the Specular and Magnetic ores. Overlying these beds is 
usually found a quartz rock, which is probably one of the most recent of the 
district. Below the Specular is a green stone, often slaty, and beneath 
this are one or more horizons of the Flag ore, separated by crystalline 
schists. Next older than the Flag ores is another quartzite, which seems to 
be sometimes replaced by a silicious marble. Yet older are the granite^rocks, 
which are supposed to belong to the Lawrentian system of Canada — the 
schists above named, including the ores, belonging to the Huronide system. 
