208 The American Geologist. March, 1892 
a mile to about three miles, is underlain, on the south by a complex 
group of granites, gneisses, and schists of Archean age, and is overlain on 
the north by the interbedded eruptive and fragmental rocks of the 
Keweenawan series, the whole section having a steep northward dip. 
The Penokee and Keweenawan series are classed together as belonging 
to the recently named Algonkian period, between the Archzean or Lau- 
rentian and the Cambrian or Taconic, nearly equivalent to the Huronian 
period of the Canadian geologists. 
A cherty limestone, attaining a maximum thickness of 300 feet, is the 
lowest member of the Iron-bearing series in the Penokee region. 
Whet er it was originally of chemical or organic origin is undetermined, 
but it gives no evidence of having been fragmental. 
The next member, called quartz slate, is a detrital formation, averag- 
ing about 450 feet thick. 
Upon this rests the iron-bearing member, in which all the known ore 
bodies occur. It is mainly about 850 feet thick, and consists of slaty and 
often cherty iron carbonate, ferruginous slates and cherts, and actinolitic 
and magnetitic slates. All these rocks are believed to have had a 
chemical or organic origin, none being accumulated as mechanical 
detritus. The ores are soft, red, somewhat hydrated hematite, derived 
by concentration from the lean carbonates of the formation through the 
action of infiltrating surface waters during or after the uplifting and 
partial erosion of the series. 
Succeeding next above these strata is the upper slate member, the 
highest of the series, which in places is several times as thick as the 
three lower members combined. It is a slate or mica schist, chiefly 
composed of quartz and feldspar, and thin sections usually reveal its 
fragmental character. 
The four divisions are conformable with each other through all their 
extent. Many dikes of diabase, varying from a few inches to ninety feet 
in width, intersect the series, which also in some portions contains 
interbedded sheets of diabase, apparently intrusions rather than over- 
flows. 
Hlements of Crystallography, by Gro. H. WittiAMs, Pu. D. Second 
edition. New York. Henry Holt © Co. 1891. 
Lhe appearance of a second edition of the ‘Elements of Crystallo- 
graphy” so soon aiter the issue of the first, is the best proof of the need 
which has existed for such a book. Hitherto there has been no satisfac- 
tory exposition in the English language of elementary crystallography, 
if we except, perhaps, Bauerman’s “Systematic Mineralogy,” which has 
not met with favorable acceptance in this country, aad which in some of 
its features is objectionable as a book for beginners. With the growth 
of the science of mineralogy, particularly on its physical side, with the 
increasing interest among chemists in the relations between chemi- 
cal properties and crystallographic form and with the rapid modern de- 
velopment of petrography as one of the most important departments of 
seological science, there has sprung up in these various departments of 
