Chemical Origin of Iron Orcs^ Etc. — Winchell. 293 
proximity to the ore. But, instead, some part of the silica 
found in strata distant from the ore lodes is in the form of 
rounded grains of vitreous quartz such as is chemically depos- 
ited in ordinary quartz veins. Besides silica, an aluminous 
element also displays itself in the formation at points removed 
from the mines. 
Another noticeable difference between the Huronian and 
the Keewatin ores consists in the gradual changes that are seen 
to occur in the Keewatin ore as the country rock becomes more 
and more crystalline, massive and diabasic. In passing east- 
ward from Tower the hematite is seen to give place gradually 
to mugnQiiie, pari passic^ as the green schists assume the char- 
acter of unmodified diabase ; and in the vicinity of Snowbank 
lake the iron ores are magnetic jasperoid lodes embraced in 
such massive diabase," conforming in general with the strike 
of the rocks of the region, and still showing all their necessary 
relations to the Keewatin formation. These characters 
are found, not in the lower, often lake-filled valleys, but on the 
hills at elevations of several hundred feet. No such phenom- 
ena have ever been reported from the Huronian. The erup- 
tive, diabasic rock of the Huronian mines, either underlies the 
iron-bearing strata unconformably, as described by Dr. 
Rominger, or is in the form of transverse dikes that cross both 
the country rock and the ore beds, as recently described ^ by 
Van Hise. 
Not only in respect to age and geological relations do these 
ores differ, but chemically they are quite different. The points 
of dissimilarity stand prominent in making a comparison of 
their impurities. The Keewatin ores contain silica as their 
chief impurity, the amount of phosphorus, determining the 
Bessemer or non-Bessemer grade, not being noticeably differ- 
ent from the Huronian ore. But in respect of other impurities 
the Pluronian ores contain about 300 per cent, more manga- 
nese, about 400 per cent, more sulphur, about 33 per cent, more 
alumina, about 25 per cent, less of magnesia, about 400 per 
cent, more lime, and about 400 per cent, more water.*^ The 
Huronian ore is generally soft, and sometimes is a limonite 
passing to siderite. The Keewatin ore is hard, never limonitic, 
and has not been known to contain any carbonate of iron. 
* Am. Geol. Jan. 1889. p. 19; 17th Rep. Minn. Sur. p 122. 
^C. R. Van Hise. Avi. Jour. Set. (in.) xxxji. p. 32. 
