INTRODUCTIOIsr. 



XXV 



varieties of metamorpliism in various stages of advancement. The working 

 out of the details of the transformations of the different kinds of rocks 

 during their processes of metamorphism is one of the chief scientific results 

 which has come from a study of the district. 



CORKEIjATION. 



In order to compare the succession in the Crystal Falls district with 

 that in the adjacent Marquette and Menominee districts, the descending pre- 

 Cambrian succession in each of the three districts is here given in parallel 

 columns, the formations which are thought to be equivalent being placed 

 opposite one another : 



Descending succession of formations in the Marquette, Crystal Falls, and Menominee districts. 



MARQUETTE DISTRICT. 



Upper Marquette. 



(1) Michigamme formation, bearing a short 



distance above its base an iron-bearing 

 borizon, and being replaced in much 

 of the districtby the Clarksburg vol- 

 canic formation. 



(2) Ishperaing formation, being composed of 



the Goodrich quartzite in the eastern 

 part of the district and of the Goodrich 

 quartzite and the Bijiki schists in the 

 -western part of the district. 



Unconformity . 

 Lower Marquette. 



(1) Kegaunee iron formation, 1,000 to 1,500 



feet. 



(2) Siamo slate, in places including inter- 



stratified amygdaloids, 200 to 625 feet 

 tbick. 



(3) Ajibik quartzite, 700 to 900 feet. 



(4) Wewe slate, 550 to 1,050 feet. 



(5) Kona dolomite, 550 to 1,375 feet. 



(6) Mesnard quartzite, 100 to 670 feet. 



CRYSTAL FALLS DISTRICT. 



Upper Suronian. 

 (1) Michigamme formation, bearing' 

 a short distance above its base 

 an iron-bearing horizon. 



(2) Quartzite in eastern part of dis- 

 trict. 



Unconformity . 

 Lower JSuronian. 



(1) The Groveland formation, about 



500 feet thick. 



(2) Hemlock volcanic formation, 



1,000 to 10,000 feet thick. 

 In western part of district also 

 occupies the place of (1) and 

 (3). 



(3) Mansfield formation, 100 to 



1,900 feet tbick. 

 (4) Eandville dolomite, 500 to 1,500 



feet thick. 

 (5) Sturgeon quartzite, 100 to 1,000 

 feet thick. 



MENOMINEE DISTRICT. 



Upper Menoninee. 

 (I) Great Slate formation 



Unconformity. 

 Lower Menominee. 

 (1) Vulcan iron formation con- 

 taining slates. 



(2) Antoine dolomite. 



(3) Sturgeon quartzite. 



Unconformity . 

 Archean. 



Unconformity. 

 Archean. 



Unconformity. 

 Archean. 



From the three columns it appears that the equivalents in the different 

 districts can be made out with a considerable degree of certainty. There 

 are, however, various differences, due to several causes. 



For Upper Huronian time, omitting the Clq-rksburg formation, the sue- 



