DISCUSSION OF CORRELATION 721 



Huronian. If the Presque Isle and Wolf Lake granites are of 

 the same age, it follows that the Paint formation is Middle 

 Huronian.^ 



In the argument for retention of present correlations which 

 follows, Dr. Leith is unable to accept the correlation of the Vulcan 

 series of the Crystal Falls-Iron River district with the Negaunee 

 series of the Marquette Range, for the reason, among others, that 

 the Vulcan iron formation occurs in lenses in slate, as against the 

 well-defined position of the Negaunee formation in the strati- 

 graphic succession. In this connection it should be observed that 

 this dissimilarity of occurrence is fully as great and of the same 

 order in comparison with the Animikie series of the Gogebic, 

 Mesabi, and old Menominee ranges with which the Vulcan is cor- 

 related by him as well as by me. If the observation is of 

 importance in the one case, is it not equally so in the others ? 



In further reference to the correlation of the Negaunee and 

 Vulcan iron-bearing series, it may be observed that the Negaunee 

 series in the Marquette trough is thick and well developed and 

 should be expected to occur in the down folds over a large area. 

 The Ajibik quartzite has a maximum thickness of 700-750 feet, 

 the Siamo slate probably from 500-600 feet, and the Negaunee 

 iron formation in excess of 1,000 feet. The Siamo slate is not 

 persistent on the south side of the trough west of the latitude of 

 Ishpeming, where the Negaunee rests directly on the Ajibik quartz- 

 ite. The Negaunee formation, as well as the underlying quartzite, 

 becomes thinner in this direction, and in the Sturgeon trough and 

 around the great anticline in the Crystal Fails district the Ajibik 

 formation, according to the latest maps of the United States 

 Geological Survey (191 1), is entirely absent, the Negaunee forma- 

 tion there resting directly on the Lower Huronian. The correlation 

 of the Vulcan formation of the Crystal Falls district with the Ne- 

 gaunee formation of the Marquette district is criticized by Dr. 

 Leith on the basis of the apparent absence of the Ajibik quartzite 

 in the former area. However, the Ajibik formation is known to have 

 disappeared from beneath the Negaunee in the direction of the Crystal 



^ R. C. Allen and L. P. Barrett, " Contributions to the Pre-Cambrian Geology of 

 Michigan and Northern Wisconsin," Publ. 18, Mich. Geol. and Biol. Survey (in press). 



