PUBLICATIONS. ANG) 
COMMENTS. 
This account of the Mesabi district is fairly satisfactory. The dis- 
covery of a large amount of glauconite in the least altered phase of 
the iron-bearing rock is an important additional point in the genesis 
of the rocks of the iron-bearing formations of the Lake Superior 
region. However, the conclusion that all of the iron of the iron- 
bearing formation, even in the Mesabi district, is derived from glau- 
conite hardly seems established. In the least altered phase of the 
rocks, one which shows comparatively little or no evidence of change, 
according to the analyses given, a larger proportion of the iron is in 
the form of siderite than in the form of glauconite. Also in the least 
altered phase of rock, what were regarded as original detrital grains 
of calcite or dolomite were seen. ‘These were taken to be one of these 
minerals from their cleavage, but as the cleavage of siderite is of an 
identical character, and as the analyses of the least altered phases of the 
rock show abundant siderite, and but a minute quantity of magnesium 
and calcium, it seems far more probable that this original material is 
siderite. There is no reason, so far as the writer can see, why a part 
of the iron should not have formed as siderite, and another part as 
glauconite, even in the Mesabi district itself, and it is wholly possible 
that in the Lake Superior region, in the Upper Huronian of which the 
Animikie is a part, in one district glauconite may have been the pre- 
dominant form, while in another siderite was the more abundant. 
It is of interest to note that the succession of rocks in the Mesabi 
district is the same as previously determined in the Penokee district 
and that the processes of development of the various phases of the 
altered ferruginous rocks, the agents which did the work, the resultant 
types and the concentration of the ore bodies, as given for the 
Mesabi district, are remarkably similar to those which have been ascer- 
tained to apply to other districts of the Lake Superior region.’ The 
frequent presence of the ores in basins is regarded as due to the more 
resistant character of the surrounding Keewatin rocks, rather than to 
* The Penokee Iron-bearing Series of Michigan and Wisconsin, by ROLAND DUER 
IRVING and CHARLES RICHARD VAN HisE. Tenth An. Rep., U.S. G.S., Chap. V., 
PP- 347-458, 1890, and Mon. XIX., U.S. G. S., Chap. V., pp. 182-295, 1892. 
The Iron Ores of the Lake Superior Region, by C. R. VAN HisE. Trans. Wis. 
Acad. Sci., Arts and Letters, Vol. VIII., pp. 219-223, December 1891. 
The Iron Ores of the Marquette District of Michigan, by C. R. VAN HisE. Am. 
Jour. Sci., Vol. XLIII., pp. 116-132, February 1892. 
