+ 
194 7. B. Brooks—Rocks observed in the Huronian Series, 
Art. XXV.—Classified List of Rocks observed in the Huronian 
Series, south of Lake Superior, with remarks on their abundance, 
transitions, and geographical distribution; also a tabular pre- 
sentation of the Sequence of the beds, with an Hypothesis. of 
Liquivalency ; by T. B. Brooxs. 
Durine the last ten years I have explored more or less 
thoroughly the east and north portions—about one-third—of 
the large Archean area lying southwest of Lake Superior, em- 
bracing the iron and copper regions of northern Michigan and 
Wisconsin.* Besides observations in the field, I have collected 
and catalocued over 3,000 rock specimens, mostly Huromian, 
with the rocks of Saxony. Prof. Geo. J. Brush has made seV- 
eral analyses and determinations of essential mineral constitu- 
ents. Prof. R. Pumpelly placed at my disposal bis numerous 
field-notes, made in the Archean area. r. A. A. Jali 
rom 
chiefly drawn. As many of the rocks are fine-grained, waite 
aphanitic mixtures of obscure amphibolie and feldspathic pet 
erals, the different kinds and varieties graduating — 
other, it is to be expected that similar specimens would 0 
: : is h in Te 
with the hornblendic rocks diorytes, diabases, and ¢¢ magne: 
lated chloritic: schists, also to a less extent with hydro- 
see Brooks and Pumpelly, Am. J 
Archean of Michigan, their Map No. 1, Atlas of Michigan 
ase — little of Northern Wisconsin is mapped in ome £ his labors. 
- Wichmann is preparing a: r embodying the results 0 urvey; 
$Mr. Wright’s work sik Soa ee the Wisconsin Geological Survey; 
Tesults are not yet published. 
our. Sci., vol. iii, June, 
* For geographical distribution and structural relations of the OO also ie 
— i ical Surveys — 
Sat Sap SO res hha 
but the 
