The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1904-09-02

contain profitable mines-TOwer anc
Ely-and the mines at these places are
confined to a half mile square in each
case, but the iron-bearing formation
is widely distributed throughout the
length of the district, and the i'm
portance of an understanding of the
whole district fully justifies the care
full study which was made of the
whole area.
The important fact was established
that the principal iron-bearing for
mation-the Soudan formation-be'
longed to Archean series. The adj
mission of sedimentary formation,
such as the Soudan is, to the Archean
series is one of the fundamental ad-
vances made by the Lake Superior
biologists. The Ely greensboro, a
highly metamorphosed igneous rock
probably originally andesites and
basalts-was found to be the lowest
member of the geologic column in
the district. The GRANTEES asssociat-
ed with the greensboro and the Sou
dan formation were considered young
or than either of these formations,
and established as intrusives older
than Ogishke conglomerate the basal
member of the Lower Huronian,
which SUCCEEDS the Soudan formation.
The general time of the intrusion OF
these GRANTEES and similar acid
igneousfocks is placed between the
time of the deposition of tile last
sediments Of the Archean and the de-
position of the earliest sediment of
the Lower Huronian series. The ad-
mission that all of the Ely greensboro
formation was not earlier than the
Soudan explains many relations OF
these formations which have not
been easily worked out on the prior
assumption of the absolutely greater
age of the greensboro formation.
The Lower Huronian series in this
district consists of the Ogishke con-
glomerate, Agaway formation (iron-
bearing), Knife River states, and
lastly, intrusives granite, granite
porphyries. dolerities, and lam
prophyres) proceeding upward in the
column, with an essential unconform-
ity between the Archean series and
the Lower Huronian.
The Ogishke conglomerate and
Knife River states, while important
geologically, are chiefly interesting
economically as guide to the
stratigraphy of the district. The
Agawa formation resembles the
Soudan geographically with
the important difference of the de-
velopment of iron carbOnates facies
Considerable exploration for iron has
been made in the areas in which this
formation outcrops in the eastern
part of the district, but without any
satisfactory results. Mr.. Clements is
of the opinion that no large iron de-
posits will be found in this formation
in the portion within the United
States. He considers the extension
of this formation into Ontario more
favorable. 1t may be noted that ex
plorations made last summer in thi!
extension did not show any specia
encouragement for finding iron in thu
Agawa horizon in Ontario, The in
trusive series of the Lower Huroniar
are chiefly interesting geologicall.
and because of their action on thu
adjacent formations.
The discussion of the Upper Huron
ian formation in the Vermilion dis
trict might properly be included il
the monograph on the Mesabi distrlc
as the formation, which has limited
Development in the eastern part o
the Vermilion district is distinct.
identical stratigraphically with Thu
Mesabi iron formation to the south
west. The Vermilion area has beer
locally designated as the Gunfiin
formation but corresponds with tn
Biwabik of the Mesabi district, Will
the superimposed gray-wakes ant
states, locally called Rove slate form
alton, are identical with the Virgins
slate of the Mesabi area. The Uppe
HURON rocks in the Vermilion are
are highly metamorphosed by the eX
tensiye Duluth gabbro of the Keween