leith.] WORK IN LAKE SUPERIOR IRON DISTRICT. 24VJ 
of the ores was mined by open-pit steam shovel, 46 per cent by ordi- 
nary underground methods, and 7 per cent by " milling." 
When lirst introduced Mesabi ores were considered too soft for 
extensive use in furnace charges, but now they constitute an average 
of 50 per cent of the ore burden, and individual ores may be used in 
percentages as high as 100 per cent. 
The iron and water content of the Mesabi ores is greater than in the 
other ores of the Lake Superior region. The phosphorus in the ores 
(determining their Bessemer or non-Bessemer character) is shown to 
have been introduced into the ores by percolating waters during the 
concentration of the ore and not to be a residual product of alteration. 
The precipitation of phosphorus from percolating waters is believed to 
be connected in some way with aluminous compounds in the ores. 
VERMILION DISTRICT. 
The Vermilion monograph (XLV), by J. Morgan Clements, is a vol- 
ume of 403 pages, accompanied by a general map of the Vermilion 
range covering the area from west of Tower to Gunflint Lake, an atlas 
of 24 detail maps, and 13 plates and 23 figures in text. 
The iron ores are shown to be confined to the Basement Complex 
or Archean, to be closely associated" with jasper and greenstone, and 
to have been concentrated by underground waters in steep pitching 
troughs formed by the folding of the greenstone. No direct evidence 
of the original source of the ore has been found, but it is believed 
that the iron has developed from an iron carbonate, in this feature 
resembling the old ranges of the Lake Superior region rather than 
the Mesabi range. 
The ores are hard, blue and red hematites, and up to the present 
time have been found in large quantities in only two areas in the 
district — near Soudan and near Ely. The detail maps show iron- 
formation belts at man}^ other places in the district in which explora- 
tion is warranted. 
MARQUETTE, GOGEBIC, AND CRYSTAL FALLS DISTRICTS. 
At the completion of work in the Mesabi district in 1902, C. K. 
Leith, with the direction and assistance of C. R. Van Ilise, took up 
the revision of the published geologic maps of the Marquette, Gogebic, 
and Crystal Falls districts with the jmrpose of preparing for publica- 
tion corrected editions showing the results of the vast amount of 
recent exploration, and with the further purpose of combining the 
geology shown on these maps in a large geologic map of the Lake 
Superior region, including all of the iron districts, to accompany a 
final monograph of Lake Superior geology to be submitted in 11)04 by 
C. R. Van Ilise, with the assistance of C. K. Leith. Many changes 
in the boundaries of the iron formal ions in the differen! districts 
