382 Correspondence. 
CORRESPONDENCE. 
The chemical origin of the Vermilion lake iron ores. In an 
article which is published in the November number — On a Possible 
ChemicalOriginofthelron Oresof the Keewatin in Minnesota, byN. H. 
Winchell and H. V. Winchell— the statement of opinions, as held by 
the late professor Irving and myself are so diflFerent from our true 
views that I ask that you insert in your next numbef the following : 
On page 291 the article says : 
"It is evident that the papers of the late Prof. R. D. Irving and of 
Prof. C. R. Van Hise, while in the main considering the problem from 
the point of view of the "Huronian," have also embraced in the 
scope of the phenomena cited, a group of strata much older, which lie 
everywhere unconformably under the Huronian, and which present a 
series of facts which are distinct from those appertaining to the Huro- 
nian as found in the Penokee-Gogebic and Mesabi regions. The con- 
founding of two formations, and the placing in one category the chem- 
ical and structural phenomena that are separated into two series by a 
great time interval, and by structural unconformity, have so compli- 
cated the problem that hitherto no theory has been found capable of 
covering all the facts. The existence of this widespread unconformity 
has been shown in recent reports on the geology of the northwest, by 
A. C. Lawson, A. Winchell, and by the writers; and latterly it was 
also recognized by Irving (7th An. Hep. U. S. Geol. Sur.)" 
As a matter of fact professor Irving recognized this unconformity as 
early as 1881. This is perfectly evident by his six generalized geolog- 
ical sections of the lake Superior basin, (Copper-Bearing Eocks of 
Lake Superior, page 416), in all of which the Animikie rocks are 
placed in unconformity above the gneisses and schists. Also in the 
November number of the American Journal of Science for 1887, page 
261, professor Irving describes in detail an unconformity between the 
Animikie beds in Gunflint lake and the underlying schists. This is 
the locality described by professor Alexander Winchell of the Minne- 
sota Survey several months later (Volume i, No. 1 of the American 
Geologist, pp. 14-24). 
The article assumes that the schists referred to above as occurring 
unconformably below the Animikie are the same as the rocks which 
bear the iron ores in and about Tower and Ely, Minn. This is taking 
as settled the very question at issue. To call the rocks below the 
Animikie, Keewatin, and the rocks which bear the Vermilion lake 
iron ores, Keewatin, is no evidence of equivalence. It was professor 
Irving's opinion that these formations are not equivalent; and that 
the Animikie series and that bearing the Vermilion lake ores are equiv- 
alent. The reasons for this opinion can not be given here, but refer- 
ence is made to his elaborate discussion of the whole question in the 
7th Annual Report of the U. S. Geological Survey. 
On page 294 of the article in the American Geologist is said : 
"The difficulties in applying the theory of Irving, i. e. the meta- 
somatic substitution of oxides of iron for some pre-existing carbonate. 
