Lake Superior Iron Ores.—Spurr. 335 
THE ORIGINAL SOURCE OF THE LAKE 
SUPERIOR IRON ORES. 
By J. E. Spurr, Constantinople, Turkey. 
In 1893 the author spent a few months on the Mesabi 
range in Minnesota, where he became interested in the genesis 
of the iron ores. He spent the winter working up the results 
of his trip; then, being obliged to reluctantly leave the fasci- 
nating field, he threw the results of this work into a hasty bul- 
letin, and departed. It was his hope that at some future time 
he might find opportunity to revise and extend his study, but 
fate has led him in other paths. 
After eight years of experience and reflection, the author 
is seized with the desire to use the pruning knife vigorously, 
whenever he looks at his first publication. Yet in the main 
thesis of the work—the origin of the iron ores—he still finds 
his youthful satisfaction. And the gradual] acceptance by 
most geologists of his general conclusions in this regard, to- 
gether with the circumstance that there is, among some, a slight 
misunderstanding of the details, have prompted him to write 
this sketch of his present views. 
THE LAKE SUPERIOR IRON-BEARING ROCKS. 
It is well known that the most important. iron-mining reg- 
ion in the world is near the western half of lake Superior. 
Within this region, and comparatively close together, are sep- 
arate districts or ranges,—thus called not so much on account 
of their topography as because in them the ore-bodies are 
grouped in linear arrangement, following the outcrop of cer- 
tain sedimentary formations. The Marquette, the Menom- 
inee, the Gogebic, the Vermilion, and the Mesabi ranges are 
the chief ones. The first three are on the south side of the 
lake, in Michigan and to some extent in Wisconsin; the last 
two are on the north side, in Minnesota. 
Not only the geographical grouping, but the nature, ap- 
pearance, and geologic relations of the ores in these different 
districts have marked them since the days of their earliest 
scientific investigation as belonging to a single general class 
of ore-deposits, and thus they are usually referred to as simp- 
ly the lake Superior iron ores. 
