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



In a later publication^ we will introduce evidence, based on 

 field surveys and drilling operations, in support of the correlation 

 of the Presque Isle granite with those occurring southwestward and 

 southeastward to the state line in Michigan and over an adjacent 

 large area in northern Wisconsin, possibly including the later 

 intrusive granites of the Florence and Menominee districts, hereto- 

 fore doubtfully correlated with the Keweenawan.^ The close of 

 Animikie time over this great area seems to have been char- 

 acterized by batholithic intrusions of granite on a grand scale, 

 comparable in the pre-Cambrian of the Lake Superior region to 

 those of Laurentian time. 



The Presque Isle granite is predominantly an acid type which 

 varies through gradational phases into syenite and diorite. The 

 rocks are mainly massive, but marked gneissosity is not an un- 

 common structural feature. 



Relations to Upper Huronian {Animikie) group. — -The inference 

 that the Presque Isle granite is intrusive in the Animikie group 

 rests on the following evidence : 



1. The lower members of the Palms formation show a gradual 

 transition in proportion as they approach the granite to micaceous 

 and hornblendic schists and gneisses with obliteration of clastic 

 structure. 



2. The Pahns and Iron wood formations are characterized by 

 abundant quartz veins and the Palms formation also by veins of 

 aplite and pegmatite which become increasingly prominent toward 

 the granite. 



3. The Ironwood formation becomes amphibolitic, magnetitic, 

 and schistose in proportion to approach of the granite. 



4. The Palms formation is apparently absent in the vicinity 

 of section 25, T. 47 N., R. 44 W., where the Ironwood formation is 

 an amphibole-magnetite schist and is separated by only a short dis- 

 tance from exposures of the granite. 



The foregoing relations may be illustrated by reference to a few 

 important localities. The best exposed section of the Palms formation 



' "Contributions to the Pre-Cambrian Geology of Michigan and Northern Wis- 

 consin," Publication 18, Michigan Geol. and Biol. Survey (in press). 

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



