686 A. C. LANE AND A. E. SEAMAN 
greenstone schists, and it must not be forgotten that the Minnesota 
Survey has held it to be Cambrian.t. Were the Gogebic range alone 
to be studied we might agree with Lawson, but there the unconform- 
ity at the base of the Animikie represents the elimination of all of 
the mio-Huronian and most of the eo-Huronian, thus representing a 
good part of Huronian time. Without question the Animikie is much 
less disturbed than the older formations, but we are not prepared to 
say that any one of the breaks before the Keweenawan is the “‘essen- 
tial break.’’? 
The divisions are: 
a) Goodrich quartzite. ‘This is represented on the Gogebic range 
by the Palms formation of red and green quartzose slates. But 
there, as on the Marquette range, there is a conglomerate base, con- 
taining pebbles of jaspilite and dolomite as well as granite. Basic 
tufaceous material is a sign of local volcanic activity, which continued 
from mio-Huronian (part of Clarksburg formation, etc.) near foci of 
which the formation may be very thick. Otherwise.......... 400 ft. 
_ 6) Bijiki formation. This is a cherty, iron-bearing member with 
graphitic slates, on the Gogebic range some 800 feet thick, known as 
the Ironwood formation and the main iron member. It was not con- 
sidered in the Marquette Monograph so persistent as we really believe 
TB STS! «asd 3.5 Sse rah eae ae sea Ocenia ats ae eee 300 ft. 
c) Michigamme slate. A group of black, graphitic slates and 
graywackes, quite wide spread—the Tyler slate of the Penokee- 
Gogebic range, the Lake Hanbury slates of the Menominee Range. 
Usually not over 1,000-2,000 feet thick. On the Gogebic range 
apparenthy:s lc Ruck Acre eee ees Sores PN Loreena 4,000 ft. 
Keweenawan.—This term used as a technical name for a rock 
series is nearly synonymous with Nipigon, which has a year or so 
priority, but was introduced practically simultaneously in two slightly 
different senses; and the term Keweenawan has been so much more 
widely used that the joint committee agreed to retain it. Douglass 
Houghton included the Lower Keweenawan up to the Great Con- 
t But Logan and Hunt in the original introduction of Huronian—Esquisse Géolo- 
gique, p. 28—considered Huronian as Lower Cambrian of Sedgwick. But at that 
time, as in the earlier editions of Dana, the Potsdam was classed as Silurian. 
2 Leith in A. 7. M. E. Trans., 1906, p. 128. 
