748 Oo KG AIGIEMITEL 
tions, and are not repeated.* The succession in the Menominee dis- 
trict of Michigan, as given by Smyth,’ is compared with that of the 
Marquette district, and points of similarity and difference noted. It 
is shown that the series of the two districts may be roughly correlated, 
but that closer correlation may not be attempted until more detailed 
studies are made in the Menominee district. 
Newett® gives a sketch of the Marquette iron-bearing district of 
Michigan, and publishes a geological map of the district compiled from 
a map of the Upper Peninsula in the possession of the Michigan 
Geological Survey. The iron ores occur in the Huronian rocks, of 
which there are some thirty members. ‘This series of rocks has been 
subjected to enormous lateral pressure, resulting in foldings in the 
strata. In the folds the ore is found generally in lenticular masses. 
The Huronian rocks are cut by eruptive rocks, which have played an 
important part in assisting in the concentration of the ores. 
Gresley‘ describes peculiar markings in iron ore from the Chapin 
mine of Iron Mountain, Mich., which are thought by H. S. Williams, 
by Schuchert and by Walcott to be trails of organic origin. 
Comments.— At various places in the Menominee district, including 
the Chapin mine, the Cambrian sandstone unconformably overlies the 
ferruginous schists of the Huronian. At some localities the lowest 
horizon of the Cambrian is an iron ore, which has been mined. The 
question arises whether or not the organic remains referred to by 
Gresley are contained in the original ore of the Huronian or in the 
detrital ore of the Cambrian. As the specimens were found in the ore 
after it had been shipped from the district, it seems impracticable to 
answer this question, and therefore it is unsafe to conclude that the 
organic markings are of pre-Cambrian age. 
‘Correlation papers—Archean and Algonkian, by C. R. VAN Hise. Bull. 
U.S. Geol. Sury., No. 86, 1896, pp. 183-186. 
Principles, cit., pp. 796-799. 
2The Lower Menominee and Lower Marquette series in Michigan, by H. L. 
SmMyTH. Am. Jour. Sci., 3d series, Vol. XLVII, 1894, pp. 216-223. 
3The Marquette Iron Range of Michigan, by G. A. NEWET?. Proc. Lake 
Superior Mining Inst., Vol. III, 1895, pp. 87-108. With geol. map. 
4Organic markings in Lake Superior iron ores, by W. S. GRESLEY. Science, 
new series, Vol. III, 1896, pp. 622-623. 
