CONTRIBUTION TO THE PETROGRAPHY OF THE 

 KEWEENAWAN^ 



FRANK F. GROUT 

 University of Minnesota 



OUTLINE 



Introduction 

 Geology: Surficial 



Relations 

 Structure 

 Areal 

 Economic 

 Petrography: Review 



Clastic Rocks 



Types of Igneous Rocks 



Mottled Diabase 



Hackly Diabase 



Conchoidally Fracturing Diabase 



Porphyritic Variations 



Glasses 



Amygdaloidal Textures 



Amygdules and Other Secondary Rock Minerals 

 Chemical Classification 



INTRODUCTION 



The effusive and clastic rocks of the southwestern extreme of the 

 Keweenawan area, reaching into Minnesota, have been the subject 

 of new study, more detailed than is reported in previous papers.^ 

 The main results are of two kinds, detail of outcrops, and a laboratory 

 study of rock types and minerals, the latter of more general interest 

 than the former. The new detail reveals no great error in the general 

 maps recently published, but the map here presented shows the 



I By permission of the Minnesota Geologic and Natural History Survey. 



2R..D. Irving, "Copper-bearing Rocks of Lake Superior," U.S.G.S. Mon. V; 

 Warren Upham and N. H. Winchell, Minnesota Geol. and Nat. Hist. Survey, II and 

 IV (county reports); C. P. Berkey, "The Geology of the St. Croix Dalles," American 

 Geologist (1897); C. W. Hall, "The Keweenawan Area of Eastern Minnesota," 

 Bull. Geol. Soc. Am., XII, 313. 



633 



