196 T. B. Brooks—Rocks observed in the Huronian Series, 
EXPLANATIONS, 
1st. The numbers following many names refer to typical 
specimens of that rock contained in my Michigan State Collec- 
vol. ti, p. 201), partial duplicate suites of which were furnished 
the University of Michigan, Boston Institute of Technology, 
2d. Those rocks marked L have also been observed in the 
Laurentian system, which has however been but little explored. 
No Huronian rocks are believed to be identical with those of 
the copper-bearing series, although some of the greenstones 
have considerable resemblance. : : 
: e Marquette region embraces the important iron-min- 
ing district southeast of Keeweenaw Bay; of which Marquette 
in Michigan is the chief port. About fifty or sixty miles south 
is the undeveloped Menominee iron region extending into Wis 
consin. One hundred and twenty-five miles west of Marquette, 
on Black River, Mich., and thirty miles farther west, where 
Bad River crosses the Penokie Iron Range, Wis., the Huronian 
series is well exposed. See table. ; 
4th. The Roman numerals of the table express the approxt 
mate relative age of the twenty beds into which it has > 
found convenient to divide the Huronian of the Marquette 
Menominee regions, numbered from the oldest upward. : 
equivalency has been extended with less certainty to the Blac 
River and Bad River series, and with still less to the Huroman 
of Canada. See table, : 
5th. The names of rocks which have not been observed 12 
the Huronian are usually printed in italies. oth 
th. The varieties of each kind of rock are arranged in t 
order of relative abundance, so far as known. 
1. FRAGMENTAL Rocks, EXCLUSIVE oF LIMESTONES. 
scur in 
Tr ue quartz-conglomerates are not abundant, but — o 
the Middle Huronian, both in the Marquette and Menom 
Regions ; and in the latter, at the base of the series, ¥* 7 pie 
gine conglomerate holding pebbles of granite, gneiss, 40 y geee 
ie oy revised and extended descriptive catalogue of this 
ei mneo WY much extended, is in course of preparation. 4 
_ +The specimen numbers in italics were selected by Dr. Wichmann 38 Pos 2 
Beye, Steatest lithological interest. Duplicates have been given 
» from which I understand he will furnish mounted thin séctions. 
