216 II. L. Smyth — Lower Menominee and 



Art. XXI. — delations of the Lower Menominee and Lower 

 Marquette Series in Michigan {Preliminary) ; by Henry 

 Lloyd Smyth. 



Nearly all writers on Michigan geology from Brooks to 

 Wadsworth have maintained the general equivalence of the 

 Marquette and Menominee iron-bearing series.* 



This opinion has been founded on the similar unconform- 

 able relations of the two series to an undoubtedly older crys- 

 talline complex, and on a general lithological similarity between 

 some of the individual members. 



It is the object of this paper to review briefly the evidence 

 by which this correlation has been supported, and to present 

 some new facts that appear both to modify and to give it a 

 more definite shape. It should be remembered that the rocks 

 of the two series have never been traced into each other, and 

 that until recently there has been an unbridged gap many 

 miles wide between them. 



General Relations. 



So long as the iron-bearing rocks of Michigan were thought 

 to constitute an uninterrupted succession, the argument from 

 similar relations to similar older rocks had much force. It was 

 further strengthened by Yan Hise's discovery that the Mar- 

 quette series was divided into two unconformable series, and 

 by his later announcement, that the Menominee series was 

 probably similarly divided by an unconformity. More recent 

 and extended work in the northern extension of the Menominee 

 area has so far confirmed these views that it is now certain 

 that the Menominee rocks are made up of an upper and a 

 lower series, separated by an unconformity. 



The general relations in the two districts are given in the 

 table below, which differs from that given by Yan Hise in 

 Bull. 86, IT. S. G. S., in the substitution of Upper and Lower 

 Menominee for Western Menominee, and Menominee Proper. 



*In order not to re-state views that are already so well known, the reader is 

 referred to the following list, which does not pretend to be exhaustive as regards 

 either authors or titles : 



Brooks, Geol. Wisconsin, vol. iii, p. 450 table.— Greduer, quoted in Bull. 86, 

 U. S. Geol. Survey, p. 90. — Irving. 7th Ann. Rep. U. S. Geol. Survey, p. 435. — 

 Van Hise, Bull. 86, U.S. Geol. Survey, pp. 197-8.— Wadsworth, Report State 

 Board of Geol. Survey, Lansing, Mich., 1893, pp. 104, U7. 



