56 THE PENOKEE IROX-BEAKING SERIES. 



In some of tbein the crystals of labradorite are 2 inches across; in tact, this min- 

 eral in nearly all of them is the principal one. A weathered snrface of the rock is 

 fi'equently rongh and knotty, with projecting grains of titanic iron ore. The angite 

 is best recognized under the microscope. The diorites are also massive. The coarser 

 varieties are easily distinguished from the diabases by the cleavage planes of the 

 hornblende. (Pp. 248-255.) 



With Mr. Wright's views, thus indicated, as to the unconformities 

 between the slaty series and the gneissic and diabasic rocks which respec- 

 tively underlie and overlie it, we are in entire accord. With his schemes of 

 stratigraphy for the Iron series, and of the equivalency of its members 

 with those marked out liy Brooks for the Marquette Iron-bearing series, 

 we are in many respects unable to agree, as will appear hereafter. 



Hunt (T. S.). The History of Some Pre-Oambrian Rocks in Aun>rica and 

 Europe. Am. Jour. Sci., M series, vol. xix, ISSO, pp. 208-283. Read before the 

 American Association for the Advancement of Science, Sept. 1, 187!). 



This paper maintains the Neptunean origin of the Archean and crys- 

 talline schists, including also the " olivines and serpentines, and, in short, 

 all silicated crystalline stratified rocks." It gives also an outline historical 

 account of the pre-Cambrian formations. In the course of this account a 

 brief reference is made to the views of Foster and Whitney maintaining 

 the nondivisibility of the lake Superior Archean, and to the opposing 

 views of Logan, Murray, Kimball, Credner, Brooks, Pumpelly, and 

 Irving, the author himself maintaining a divisibility into two distinct ter- 

 ranes. No specific reference to the Penokee region is made, but since it 

 aifords most abundant proof of such a divisibility, Hunt's essay mav ajjpro- 

 priately be noticed hei'e. 



Wadsworth (M. E.). Notes on the Geology of the Iron and Copiier Districts 

 of Lake Snperior. Bull. Mus. Comp. Zool, vol. vii, 1880, No. 1, Cambridge. 



So far as the Iron-bearing rocks are concerned, the main oljjects of 



this volume are to set forth certain observations and conclusions with 



regard to the rocks of the Marquette Iron region of Michigan. Since the 



Penokee rocks were already at that time, by common consent, regarded as 



the equivalents of those of the Marquette region, the conclusions are 



extended to the former rocks also. The following quotations will show 



what the principal ones of these conclusions are. 



