292 Chemical Origin of Iron Ores, Etc. — Winchell. 
Rep. U. S. Geol. Sur.) By Prof. Irving, however, there had not 
been, prior to his death, so far as known, any reconstruction 
or linaitation of his general theory of the origin of the iron 
ores. 
It is the purpose of this paper, while not calling in question 
the explanation by Irving of the origin of the ores of the 
Huronian, to show specifically a possible origin for those of 
the Keewatin as they are found in the Vermihon range in 
northeastern Minnesota. 
That there is reason to account for the Vermilion ore on a 
different hypothesis from that which may be sufficient for the 
Huronian ore, is evident from a consideration of the follow- 
ing differences in the formations : The Huronian strata are 
of fragmental origin, accumulated by the slow process of sedi- 
mentation and are siliceous ; being banded by lines of depo- 
sition that fade from one sort to another by such insensible 
transitions as can be produced by successive variations in the 
forces of an ordinary sedimentary process. This structure 
not only pervades the rock that embraces the ore, but passes 
into the ore itself. The formation as a whole, and certainly 
the beds that embrace the ore, are made up of secondary 
grains derived from some other formation. In other words it 
is non-crystalline. (Irving, 3rd An. Rep. U. S. Geol. Sur. pp. 
157-165; 16th Report, Minnesota survey, p. 39.) 
On the other hand the strata that carry the iron ore deposits 
of the KeeAvatin are,when not rotted in situ, crystalline or sub- 
crystalline, and do not vary in composition like a sedimentary 
rock. They do not show except very rarely, any transitions 
between the ore and the enclosing rock, and when they do 
show such a mingling the alternations are between two kinds 
of materials, and without intermixture of clayey substances. 
The two materials are the ore itself and the country rock. 
But the country rock is uniformly constituted of diabasic 
schist which shows either its direct origin from eruptive, basic 
rock or its quick distribution and deposition in waters heated 
by volcanicjdisturbances ; and but rarely has so much inter- 
mingled silica, of secondary sedimentary derivation, as to 
raise the per cent of silica above the limit of Von Cotta for a 
basic rock. At points remote from the ore lodes the propor- 
tion of silica increases, and it is besides not wholly of the 
characteristic chalcedonic sort that prevails in the ore and in 
