PUBLICA TIONS. 223 
occur in the Penokee series came up partly, at least, before the enclos- 
ing rocks assumed their present position, and they have since been 
subjected to the same disturbance which developed the monoclinal 
structrue of the region. ‘The result is that in places where the dikes 
intersected the quartzite of the Quartz-Slate series V-shaped troughs 
have been formed, opening upwards and bordered on one side by dia- 
base and on the other by quartzite. In these troughs, of course, were 
originally included V-shaped masses of the cherty iron carbonates of 
the Iron-bearing member which immediately overlies the quartzite. 
This material contained too little iron to be of cominercial value, but 
by a process of chemical concentration in the V-shaped troughs, rich 
bodies of pure hematite have been formed. It is shown that during the 
process of erosion and superficial oxidation one side of the V-shaped 
mass of cherty iron carbonates was oxidized more rapidly than the 
other, so that the iron in it was converted to sesquioxide, while the 
iron in the other side was still in the form of carbonate. Surface 
waters percolating through the oxidized part of the V-shaped mass, 
therefore, continued down without losing much of their oxygen, for 
the materials which they met in their course had already been oxidized. 
These waters in descending met one of the sides of the V-shaped 
trough and were deflected down to where the two sides met, with con- 
siderable oxygen still in solution. Surface waters, however, percolating 
through the less thoroughly oxidized part of the V-shaped mass lost 
their oxygen in oxidizing carbonate of iron in the unoxidized cherty 
iron carbonates, but in turn they received carbonic acid from the decom- 
posed carbonate. This enabled them to dissolve some of the iron car- 
bonate not yet decomposed ; and thus ladened with iron in solution, 
they percolated down, and were deflected by the other side of the 
trough into its lower part. Here they met the waters containing oxy- 
gen which at once oxidized the iron held in solution and precipitated 
it in a sesquioxide condition. In this way the large bodies of iron ore 
were collected; and by the same waters that brought the iron into the 
trough the silica in the cherty material was removed, thus leaving a 
pure iron ore. It is evident that during the erosion of the cherty iron 
carbonates the iron from them would be gradually leached out and car- 
ried into the trough, instead of lost in surface waters. 
The evidence that such a process has gone on is very strong and 
has been presented in a most admirable inanner by Professor Van Hise, 
whose work shows very clearly the fallaciousness of the old idea that the 
