Chemical Origin of Iron Ores, Etc. — Winchell. 295 
i. e. during the age of the Vermilion and of the Keewatin, may- 
be fairly apprehended, and brought to bear upon this inquiry, 
it will be necessary to mention some inferences that have 
recently been wrought out by the study of the Archean/' 
It has been stated repeatedly by G. M, Dawson,'" by A. C. 
Lawson" and by the writers,'- that the rocks of the Keewatin 
consist very largely of volcanic ejectamenta. These ejectamenta 
were received in oceanic waters. The volcanoes themselves 
were mainly sub-marine, and the products of any intervening 
stage of sedimentary quiet were buried under the lavas of the 
next quickly succeeding stage of eruption. Whether this erup- 
tive age was world-wide, in its production of this kind of basic 
schist, as seems very likely, it is not necessary here to inquire ; 
but that it was one of long duration, and prevailed in all of 
northeastern Minnesota wherever this rock horizon has been 
examined, and extended into Manitoba, there is no longer any 
room to doubt. It is therefore necessary to inquire how such 
products as chalcedonic silica and hematite could have been 
formed in a sea that was at times seething and steaming Avith 
volcanic craters and earth fissures from which escaped molten 
rock from below the thin crust. That this chalcedonic 
silica, involved closely with interbanded hematite, and grad- 
ing to hematite by insensible variations in the amount of iron 
present, was received in water and distributed by water is 
indicated not only by the stratiform arrangement, but also by 
the presence, occasionally but very rarely, of rounded grains 
of other silica, not chalcedonic, some of them being a quarter 
of an inch in diameter, embraced in the general mass of the 
jaspilyte, and sometimes forming more or less distinct bands 
or pebbly patches in the jaspilyte, approximately parallel with 
the general strike. This fact effectually vetoes the eruptive 
theory, and demonstrates that there was no exception in favor 
of that theory so as to produce a structure characteristic of 
sedimentation, through the agency of molten acid lava fiows. 
When the character of some of the narrow bands of pure 
^Seventeenth Anmial report Miiinesoia survey, pp. 37-40. 
^^ Geology and Resources of the 4^th parallel. 1875. p. 52. 
" Geology of the Lake of the Woods. Can. Survey Eep. 1885. C. pp. 49- 
54. 
^-Fifteenth Report, Minnesota survey. 1886. p. 221 ; Sixteenth Report, 
p. 108; Seventeenth Report, p. 37; Am. Geologist, Jan. 1889. vol. in. 
p. 22. Compare also Foster & Whitnej- on the "Azoic ;" Report on the 
lake Superior land district, 1851. Partii. p. G7. 
