Beview of Recent Geological Literature. 327 
kian. The introduction of a new name, witli tlie uncertain upward 
and downward limitations wliicli are said to bound tlie application of 
this, is unfortunate for American geology, for while adding nothing to 
the definiteness of other terms, its own existence is founded on uncer- 
tainties both at the top and at the bottom. To assign a terrane to the 
"Algonkian" is worse than to assign it to the Huronian. The latter 
term is beginning to acquire some delimitation. It is now known to 
embrace two great formations, and originally embraced three. These 
three are now covered by the new term, but the new term goes lower, 
inasmuch as it descends to the lowest recognizable sediments. It e.\- 
tends from the base of the Cambrian, wherever that may be, to the ho- 
rizon of the lowest recognizable sediments. 
There are two topics discussed in this work to which it would be well 
to call attention: 1st, the cherty carbonate, and 2d, the origin of the 
ores. 
The cherty carbonate has played a very important and rather curious 
role in the literature of the Penokee region. From being considered the 
basal member of the Huronian (i. e. the true Huronian according to 
Irving, the upper Huronian of Van Hise,) and the source of the iron 
ores of the region by a process of chemical change and concentration, 
it is now removed from the Upper Huronian and put into the Lower 
Huronian, constituting there its sole representative. and is relieved from 
its responsibility for the origination of the iron ore. The facts on which 
Van Hise now puts this in the Lower Huronian were known b.y Irving, 
but he did not consider them as sufficient to warrant the interposition 
of so profound a break above the limestone as this volume expresses. 
The fact that the strike of the limestone is identical with that of the 
iron-bearing and the quartz-slate members points to the essential con- 
cordance of the limestone with the Upper Huronian. It is, to say the 
least, a rather singular member of the Penokee series. It is wanting in 
places on the north side of lake Superior in the same manner, indeed it 
is hardly known in Minnesota, but reaches a large development about 
Thunder bay. 
As to the origin of the iron ore uf the Penokee range, it is in the first 
instance found in a "cherty iron carbonate," separated by several hun- 
dred feet from the foregoing "cherty carbonate." From this condi- 
tion the rock passes by chemical transformations to ferruginous slates 
and cherts and to actinolitic and magnetitic slates, the ores themselves 
being secondary concentrations found at the lowest horizons. Mr. J. E. 
Spurr, when examining the equivalent ores of the Mesabi iron range for 
the Minnesota Geological Survey, after careful microscopic researches, 
reached the conclusion* that the cherty iron carbonate is itself a sec- 
ondary rock, and that the real .source of the ore is in a glauconitic sand 
which, being in unstable chemical condition, gave origin both to cal- 
cite and to hematite. This rock, in its original cojidition, is greenish, 
but easily becomes red, or reddish. It then appears to consist of amor- 
phous silica in which float blood-red globules. The globules are some- 
*BuUetin X of the Minnesota Survey. 
