252 The American Geologist. October, 1903. 
Huronian is characterized by a great conglomerate which lies on the 
"Archean," but above the conglomerate, as described by the Minnesota 
survey, are great thicknesses of finer detritals. The Upper Huronian 
(i.e. the Animikie) is divided into three parts. To the lowest part the 
term Pokegama quartzyte is applied, having a thickness from zero to 500- 
feet. This is the term used by the Minnesota survey for the same form- 
ation. Next higher is the Biwabik, or iron-bearing member of the Ani- 
mikie, and above that is the Virginia slate. An important fact is em- 
phasized here by the author, viz : the non-conformity of the Biwabik 
member on the Pokegama quartzyte. This had been noted by the Min- 
nesota survey (by Spurr), but its generality and significance had been 
overlooked. At the base of the Biwabik is a series of "conglomerates 
and quartzytes," from a few inches to fifteen or more feet in thickness, 
which pass upward into the ferruginous rocks of the Biwabik rather 
abruptly. The relations indicate a brief erosion interval between the 
Pokegama and the Biwabik. The average thickness of the Biwabik is 
estimated at 1000 feet, but the actual thickness varies from 200 to 2000 
feet. 
The Virginia slate is apparently only an upward and very extended 
enlargement of slates that begin in the Biwabik. "The slate grades, 
both vertically and laterally, into the Biwabik formation." It is hence 
very uncertain where the line separating the two subdivisions should be 
drawn, either areally or stratigraphically. 
The Keweenawan rocks are briefly described in the usual terms. They 
embrace gabbro, diabase, and granite, all intrusive into the rocks with 
which they come into contact. In regard to the granite of the Keween- 
awan the author describes it as forming a part of the Giant's range, and 
as intrusive into the Animikie. Should this conclusion be sustained by 
future observers it would be a confirmation of the view of H. V. Win- 
ched that the Giant's range was elevated since the deposition of the 
Animikie iron ores. Mr. Leith's description of the intrusive contact 
of the granite on the slates of the Animikie is not sufficiently conclusive. 
It appears to the writer that, though there are two dates of granite in 
the Giant's range in the vicinity of Birch lake, as fully identified and 
described by him, yet they may both antedate the Animikie. Some of the 
facts mentioned by the author as indicative of intrusive action are clearly 
and necessarily to be referred to fragmental contact at an unconformity 
of the Animikie on the Archean, and that fact throws a doubt on his 
interpretation of the rest. 
The Cretaceous, which exists on the Mesabi range in isolated areas, 
is also described. In respect to the Pleistocene deposits, the author 
states : "Several remarkable steep-walled gorges through the crest of the 
Giant's range at high elevations are believed to be the work of Glacial 
. streams escaping from a great lake ponded between the Giant's range 
and the ice-front when the glacier had drawn back from this area." 
The most interesting chapters, and those in which the author has 
shown skill in observation as well as accuracy in description, are those 
