248 ■ The American Geologist. October, 1904. 
In Minnesota this ferrodolomyte as a rock mass is more nearly 
a dolomitic sideryte. 
The author fully considers the subject of underground 
water and its agency as a possible producer of this ore, as has 
been urged for the other ores of the lake Superior region. By 
the steps of such investigation such origination is excluded, 
because, ( i ) the minerals in solution in the underground 
waters are not noticeably different from those in solution in 
surface waters; (2) the minerals deposited in the overlying 
sandstone are not iron but silica and lim^, the latter in small 
amount; (3) river waters often hold in solution iron in greater 
quantity than is now contained in the underground water of 
the Baraboo district; (4) the iron in underground waters is 
held in solution tmtil the waters are exposed to the oxidizing 
action of the atmosphere at the mouths of springs ; or by the 
action of iron bacteria: (5) the iron of the formation was de- 
posited prior to the formation of the numerous quartz veins 
that penetrate the beds, i. e. prior to the upheaval and tilting 
that fractured the strata; (6) these veins are quartz, with 
very small amounts of lime and of iron sulphide, and they 
must have been formed by underground waters; (7) the rela- 
tions of the ore to the containing rocks in everyway indicate 
that the ore originated cotemporary with the deposition of 
the rocks as sediments. 
As to the origin of the ore the author states that he be- 
lieves that it was originally a deposit of ferric hydrate, or 
limonite, formed in comparatively stagnant and shallow water. 
under conditions similar to those existing when bog or lake 
ores are being formed to-day, and that such ore has been 
altered by heat and pressure to hematite. He also believes that 
organisms played an important part in the formation of the 
strata of hematite, as well as of the strata of dolomyte and 
chert — that too, although he considers the associated recks as 
a part of the Archean (Lower Keewatin). It is the first sug- 
gestion of evidence of organic life in the Archean, excepting 
only the Eozoon canadense whose organic nature is quite gen- 
erally discredited at the present time, and whose statigraphic 
position may be considerably higher than the Lower Keewa- 
tin. and perhaps of the Lower Cambrian. The author believes 
that the shallow waters were subject to alternating changes 
