690 R. C. ALLEN AND L. P. BARRETT 



earlier workers in this field, it was thought that a field study of the 

 eastern Gogebic iron range would probably alter former inter- 

 pretations of the geology and furnish a basis of correlation with the 

 pre-Cambrian terranes of adjacent territory. 



The results of the seasons' studies are more satisfactory than 

 we had anticipated and are of considerable importance to the prog- 

 ress of pre-Cambrian geology of the Lake Superior region. This is 

 our excuse for presenting them in preliminary form in advance of a 

 more thorough treatment.^ 



We acknowledge our indebtedness to Dr. C. R. Van Hise for 

 placing in our hands his early field notes and plats, to Dr. C. K. 

 Leith for helpful suggestions in field conference, to Mr. Robert 

 Selden Rose, of Marquette, and to the Presque Isle Mining Com- 

 pany for records of drilling and underground exploration. 



SUMMARY OF THE GEOLOGY BASED ON EARLIER WORK 



Van Hise and Leith have recently presented the views of the 

 United States Geological Survey^ which may be briefly summarized. 



The Huronian rests on the Archean with profound unconformity 

 and is represented by two unconformable sedimentary groups, 

 the Upper and the Lower Huronian, which are in approximate 

 structural parallelism and dip steeply northward beneath the 

 Keweenawan. 



The Archean comprises a green schist series (Keewatin) intruded 

 by granite (Laurentian) . 



The Lower Huronian has two members, a basal quartzite 

 (Sunday) and an upper cherty dolomite (Bad River). 



The geology of the "Upper Huronian (Animikie) Group of the 

 Eastern Area" is summarized in the following words: 



In the eastern part of the district — that is, from about 6 miles east of 

 Sunday Lake to Gogebic Lake — the Upper Huronian rocks have an exceptional 

 character. In the larger part of the district the conditions were those of quiet 

 sedimentation, but in the eastern area throughout the greater part of the 

 Upper Huronian there was continuous volcanic action. In consequence the 



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

 Northern Michigan and Wisconsin," Publication 18, Michigan Geol. Survey (in press). 

 ^ Monograph 52, U.S. Geol. Survey. 



