252 The American Geologist. October, 1904. 
the Archean, amongst tlie rocks that hold the ores near Mar- 
quette, but it is plain that, if the foregoing exhibit of the 
stratigraphic relations of the Baraboo rocks be correct, tne 
Baraboo ore is chronologicall}- about equivalent to the Manitou 
epoch of the Keweenawan. 
In conclusion attention may be called to a fomier state 
ment by the writer of facts that indicate that the quartzyte at 
the falls of Pokegama on the upper Mississippi is more recent 
than some parts of the Keweenawan, and that hence it does not 
pass below the Mesabi iron ore, but may be the equivalent of 
the Puckwunge conglomerate and quartzyte. There has never 
been any demonstration of the age of this quartzyte. It is 
known to lie on the granite of the Giant's range but the age of 
the Giant's range of granite is, according to H. V. Winchell 
and Proi. C. K. Leith, later than the Aiiimikie. The age of 
the Giant's range granite has pretty generally been accepted as 
pre-Animikie, and hence Archean. Of course if it be later 
than the Animikie it will parallelize with the granite* associat- 
ed with the gabbro, and the age of the ores of the Mesabi 
range, in its western part at least, would come into question. 
At this point the facts referred to above are apropos. 
They are published in volume 5, of the Minnesota final report, 
p. 992. In making a final microscopical examination of some of 
the slides it was found that the conglomeratic portions of the 
Pokegama quartzyte which passes below the' ore at Prairie 
River falls hold a few pebbles and fragments of rock that can 
be derived only from some parts of the Keweenawan, and that 
hence some part of the iron ore of the Mesabi range, as des- 
cribed and mapped, is later than the Animikie and later than 
some part of the Keweenawan. It is a remarkable fact also 
that the rock that overlies the ore and the quartzyte, in the 
vicinity of the Diamond mine, east of Pokegama falls, is a red, 
soft, unctous shale undistinguishable from tlie shales of the 
Keweenawan that are well known. 
It hence appears probable that the stratigraphic relations of 
some of the iron ore deposits of the lake Superior region are 
not well understood and need to be re-considered. Taking 
together the facts about Pokegama falls and the new develop- 
ments at PJaraboo it seems to be pretty certain that there is an 
ore horizon in the Keweenawan about on the chronological 
