634 FRANK F. GROUT 



region of new work, the" exposures northeast of Kettle River being now 

 mapped for the first time. The Keweenawan extends not over 

 thirty miles west of the state line, and seventy miles north and south. 

 Maps on a more accurate scale will be given in the reports of the 

 survey when published. 



Acknowledgments are due to Professor C. W. Hall for the con- 

 ception of the work, and to Messrs. A. W. Johnston and W. Yeaton 

 for field assistance. 



GEOLOGY 



SuRFiciAL. — No detailed attention was given to the glacial features 

 of the area, but in passing, it was seen that a great moraine occupied 

 the southeastern side of Pine County, and that the tributaries of the 

 St. Croix River cut through a great thickness of red sandy gravel. 

 From this red drift, just south of the St. Croix, Dr. Berkey describes 

 a laminated red clay, from the study of which he draws important 

 conclusions as to the years that elapsed between two advances of 

 glacial ice. No greater exposures were found than those described 

 by Dr. Berkey, but the boundary including all such clays found in 

 Minnesota indicates that the area is about four times as great as he 

 explored (see Fig. i). 



Relations. — ^To the south, Upper Cambrian sediments lie un- 

 conformably over the lavas of the Keweenawan. To the west and 

 north, the lavas are in contact with more indurated sandstone, in a 

 fault, the mapping of which has not been much altered by the dis- 

 covery of new exposures. The correlation of the sandstone south on 

 the St. Croix, with that northwest of the fault, is considered safe, 

 but left uncertain by the fact that fossils are not known from the 

 latter, by the unknown extent of the faulting movement, and even the 

 direction of that movement. The dip of both sandstone and lava for 

 several miles from the fault is southeasterly, as would be expected 

 from an elevation of the sandstone, but observations close to the fault 

 are few, and the rocks in these cases badly shattered. When the same 

 contact is traced northeast into Wisconsin, clearer evidence points to 

 a depression of the sandstone, and this is probably the best evidence 

 of conditions in Minnesota. 



Structure. — ^Within the Keweenawan some of the structure is 

 equally uncertain on account of the scarcity of good exposures. 



