Lake Superior Iron Ores.—S purr. 341 
“Optically, the mineral has been found by professor Wolff to have 
all the characters of glauconite. 
“Tts habit, so far as can be made out, is also that of glauconite, 
in that it occurs in disseminated grains through a sedimentary bed, 
and that these grains appear to have had originally rounded outlines, 
due to attrition. 
“We must conclude, therefore, that the mineral is probably a var- 
iety of glauconite.* The characters by which it differs from the or- 
dinary mineral may be explained in two ways. In regard to the small 
amount of potash, it may either be believed that this substance was 
-absent from the original composition of the mineral, or that it has 
subsequently been removed by solution. But since its absence is ac- 
companied by the presence of iron in the ferrous condition, we find 
it difficult to believe the latter supposition; for the same agents which 
would remove the alkalies would probably effect the oxidation of the 
iron. In regard to the excess of protoxide, again, it may be believed 
either that the iron of glauconite is normally.a protosilicate, and 
that the analyses which show an excess of the sesquioxide are from 
more or less oxidized specimens; or, as seems more probable, that 
there may have been an original difference.” 
This conclusion as to the nature of the green hydrous fer- 
rous silicate was for a long time unchallenged. Recently, 
however, professor N. H. Winchell, who had formerly consid- 
ered the mineral glauconite, has brought forth arguments 
favoring the idea of a volcanic origin of the mineral.+ The 
writer regrets that he has not the report in question at hand 
at present, to go into this inquiry a little further. 
Still more recently, Messrs. Van Hise and Leith have an 
nounced that the mineral cannot be glauconite. Not having 
the original paper, the writer is obliged to quote from reviews: 
“This silicate, which occurs in green granules and is 
termed glauconite in the Minnesota reports, is here stated 
to contain no alkalies,t and thus is not glauconite,$ but a fer- 
rous silicate.” || 
“The most interesting of the late developments concern 
the origin of the iron ores. They have resulted from the al- 
teration of certain rocks containing green granules, which on 
analysis, prove to be essentially ferrous silicate. They lack 
* Italics not present in original. (J. E. S.) 
+ Final Report, Minn. Geol. and Nat. Hist. Survey, vol. v. 
ti.e¢., in PROFESSOR VAN HISE’s paper on the iron-ore deposits of the Lake 
Superior Region, 21st Ann. Rep., U. S. Geol. Sur., part iii. 
§The italics are mine. (J. E. S.) 
Review in AMERICAN GEOLOGIST, Jan., 1902, p. 51. 
