COEKELATION OF THE MAKQUETTE SERIES. 577 



characterized by bands of red jasper and specular hematite. The iron-bearing mem- 

 ber has a maximum thickness of more thau 1,000 feet, but usually it ha.s been cut 

 down greatly, or with the lower quartzite entirely, by the Auiiiiikie transgression. 



The Marquette iron ores, except those on the Upper Martiuette series, occur, as 

 Van Hise has shown, either {a) at the contact of the lower iron-bearing member with 

 the upper quartzite, when the ore may be either a concentration in the lower iron- 

 bear'ug member or a detrital member of the upper series, or, {h) more rarely, entirely 

 within the iron-bearing member of the lower series. 



These descriptions are expressed briefly in the following table, in which the mem- 

 bers of the two series are shown in parallel columns for lithological comparison: 



Menominee. Marquette. 



Michigamme jasper Jasper banded with ore. ] Iron forma- 



Slates (principal iron formation) Maguetite-actinolite schist. { tiou. 



^i^^^^oue JQuartzite. 



Quartzite I 



Archean Archeau. 



Smyth traces the magnetic Micliigamme jasper to within IJ or 2 miles 

 of the iron- bearing formation of the Marciuette series, and he regards the 

 two as eqnivalent. Toward the north the Michigamme jasper is found to 

 have a lower qnartzitic portion, which he places as eqnivalent to the lower 

 quartzite of the Marquette district. 



The whole of the Lower Marquette series would thus be represented by the high- 

 est member of the Lower Menominee. What, then, becomes in the Marquette district 

 of the great thickness of limestone, quartzite, and eruptives which lie below the 

 Michigamme jasper in the Menominee, and how is its absence to be accounted for! 



The most probable explanation is that the pre-Algonkian basement sank contin- 

 uously in both districts, but that the Marquette was initially the more elevated, and 

 as a whole was dry land, while the lower quartzite, limestone, and slates were going 

 down in the Menominee. The transgressive movement from the south reached it when 

 the lower portion of the Michigamme jasper was being deposited. 



In this discussion Smyth includes under the name Menominee the area 

 which has heretofore been called the Menominee district, and the large con- 

 necting area to the north, which is as yet largely undeveloped, and which 

 will later be described in a monograph entitled The Crystal Falls and Metro- 

 politan Iron-Bearing Districts of Michigan. For convenience in discussion 

 the term Menominee will here be used in the sense given it by Smyth. 



MON XXVIII 37 



