GEOLOGICAL EXPLOKATIONS AND LITEKATUKE— 1868. 113 



forniitx' l)etween the sandstone and tlie granite on tlie lake shore near 

 Marquette is given, and several sections are published which illustrate a 

 similar unconformitv at Granite Point, and unconi'orinities between the 

 sandstone and the Huronian beds at L'Anse, and on the lake shore south of 

 Marquette (pp. 409-411). Several of tiiese unconforinitics liad l)een known 

 as far back as Foster and Whitney's time. 



Another time interval is shown to have elapsed between the formation 

 of the gi'anitic rocks and the deposition of the oldest Huronian l)eds, pro- 

 vided the green schists of the district are separated from the Huronian and 

 placed with the granitic series, as had been advocated by the author in 

 1887. The discoi'dance between the two series "may be proved on the 

 ground bv the discordant positions of the schists of the two series, when in 

 contact or near proximity, by the large development of basal conglomerates 

 where the two foi-mations come together, by tlie indifference in position of 

 the belts of the upper series to those of the lower, by the striking contrast 

 in amounts of alteration of the upper and lower schists, and liy the totally 

 dissimilar relations of the two sets of schistose rocks to the plainh' eruptive 

 granite masses" (p. 433). Three generalized sections across the ^larquette 

 district and a re])roduction of a photographic view of a hillside 2 miles 

 south of Marquette illustrate this j)ortiou of the paper (pp. 431-43o). 



The Marquette iron-bearing series is described as abedded accumulation 

 of carbonaceous slates, ferruginous and jaspery schists, limestone, quartzite 

 and quartzite-schists, graywacke and clay-slates, and eruptive greenstones, 

 amounting in all to from 5,000 to 10,000 feet in thickness. The series is 

 separated by unconformities from the gneissic and schistose beds below 

 it, and from the Potsdam sandstone above it, and so possesses a distinct 

 iudividualitv, a foct emphasized in the paper of 1887. 



Reyer, E. Geologic der amerikaui.scLeu Eiseiilagerstiitten (insbesondere 

 Michigan). Oesterr. Zeitscbr. fiir Berg- uud Hiitteuweseu, Vol. XXXV, 1887, Xos. 

 10 and 11. Abstract in Xeues Jahrbuch fiir [Mineral., 1888, Yol. I, pages 248-249. 



The original of this article has not been seen, but from the abstract of 

 it given l^y Stelzner in the Neues Jahrbuch we learn that its author regards 

 the iron-bearing series of Michigan as an association of sediments and 



MON XXVIII 8 



