Review of Recent Geological Literal arc 251 
Lyrodesma '■>. Teclinophorus 4, Allodesma 1. Khytimya 1. Ouneamya l, 
Sp/tenolium 2, Saffordia '■'>. 
One cannot but admire tin- astuteness of observation manifested 
throughout in the treatmenl of the subject-matter, and appreciate the 
service rendered by the author toward a better comprehension of these 
fossils. The illustrations arc in photo-engraving, hut an' eminently 
sat isfactory. J. m. c. 
Tin' Iron-bearing rocks of the Mesabi Range in Minnesota. By .1. Ed- 
ward Sihkk. pp. viii. 268, with 12 plates and 22 figures in the text. 
(Bulletin Xo. 10, Geol. and Nat. Hist. Survey of Minnesota, Minneapolis, 
1894.) This monograph is by far the most important contribution so far 
made to t he geology of this recently discovered lake Superior iron ore dis- 
trict. The result of only one year's work in the Held and laboratory, it 
contains some new facts bearing on the genesis of these iron ore depos- 
its and many suggestive ideas applicable to iron ores in general. 
To the student of the geology of lake Superior iron ranges the most 
interesting portion of the bulletin is that which pies to prove that the 
original form of the iron ore was not a carbonate of lime and iron min- 
gled with more or less silica — the cherty carbonate of Irving and Van 
Ilisi — but that it was a ferrous silicate and that the cherty carbonate 
is in all instances an alteration product from this silicate and only 
one stage in its change to the final form of oxide of iron. 
Still more interesting is the suggestion that this ferrous silicate was in 
all probability the product of Poraminifera and existed as the mineral 
glauconite. The chemical analysis and petrographical si ndy of t he iron- 
bearing rocks seem to harmonize in support of this view, which, although 
not entirely original as an explanation for possible iron ore deposits, is 
yet new in its application to any particular deposits of greal extent and 
especially in rocks of such ureal geologic antiquity as those of the Me- 
sabi. It must be admitted that the demonstration will not be complete 
until the actual discovery of organic remains. Bui the author is per- 
haps deserving of so much the more credit for working out so Strong a 
case before the discovery has been made. 
The stratigraphy of the Mesabi is found to be substantial!} asgiven in 
the Twentieth annual report of the Minnesota Survey. Certain faults 
a re described in the central portion of the range which had not been 
previously noticed and for the existence of which the evidence given 
does not yet appear to be conclusive. The author argues thai the ore 
deposits have been produced along lines of fracture and weakness, and 
because he li nds ore deposits in a certain locality he si raighl wax assumes 
the presence of a fault plane there, and explains the accompanying phe- 
nomena accordingly . 
The different phases of the iron-bearing rock and their transition 
from one to another are described with such elaborate fullness as to be 
rather confusing to any hut a careful reader and student of the text; bul 
it is in such full statements of the evidence thai we find the basis for 
the conclusions drawn as to the original nature of the racks. 
