722 C. K. LEITH AND R. C. ALLEN 



Falls district, as indicated on the latest maps of this district pub- 

 lished by the United States Geological Survey. 



As to the importance which may be attached to the absence, 

 in the southern part of the Crystal Falls district, of the formations 

 which underlie the Ajibik quartzite adjacent to the iron formation 

 in the Marquette Range, it may be observed that these formations 

 appear not only on the great anticline in the northern part of the 

 Crystal Falls district but on the upturned limbs of the synclines 

 to the east — -the "eastward-projecting tongues of this great area," 

 wherein erosion has cut down into the Archean. 



Finally, it may be said that it is easier to account for the dis- 

 appearance of a coarse clastic basal member which is obviously 

 related to a shore phase of deposition than to justify, in the absence 

 of definite supporting facts, the assumption of a rather abrupt 

 disappearance of an entire series. 



It may be objected further to the correlation of the Vulcan and 

 Negaunee formations that the hard ore horizon of the upper part 

 of the Negaunee is not duplicated in the Vulcan of the Crystal Falls 

 district. This fact has little bearing on the correlation because 

 this phase of the Negaunee is related, as shown by Van Hise and 

 others, to a controlling structural condition which nowhere occurs 

 in the Crystal Falls district, i.e., it is the result of deformational- 

 metamorphic alteration adjacent to the heavy competent Goodrich 

 quartzite-conglomerate. This relationship, areally considered, is 

 entirely fortuitous and may be expected to appear only where 

 the structural conditions and deformation on which it is depend- 

 ent are in evidence. So far as lithology is concerned the Vul- 

 can and Negaunee formations are in other respects practically 

 identical. 



Dr. Leith opens his discussion of the Upper-Middle Huronian 

 unconformity at the Hemlock mine and vicinity as follows: "Prac- 

 tically no new evidence has been brought in, in the crucial area 

 between the Marquette and Crystal Falls districts, and such addi- 

 tional evidence as there is, is damaging to the conception of the 

 new hypothesis." The discovery of that unconformity has 

 apparently reversed Dr. Leith's ideas concerning the correlation 

 of the iron formation in the northern part of the Crystal Falls 

 district which he recently (191 1) correlated with the Vulcan but 



