342 C. \V. HALL KEWEENAWAN AREA OF EASTERN MINNESOTA 



Plate 28. — Profiles across the Keweenawan Series of eastern Minnesota 



FicjURE 1.. — Profile of the Snake River section. 



At Pine City a well 700 feet deep ends in wliite sandstone assumed 

 to be of Cambrian age. At the foot of Cross lake the succession 

 of lava flows comes to the surface and extends along the river for 

 nearly 3 miles in continuous exposure, dipping on an average east 

 67 degrees. Near the mouth of the Snake river the rocks dip 12 

 to 15 degrees west in a succession of lava flows which to the east 

 disappear beneath Cambrian sandstones. 



Figure 2. — The Kettle River section. 



The lava flows abut abruptly against Cambrian sandstones near 

 Hinckley, and for some miles along the river dip strongly to the 

 east. The dip changes to west 12 to 15 degrees above the big eddy 

 in section 19, township 40, range 19, and continues in this attitude 

 until the rocks disappear beneath Cambrian sandstones on the 

 Wisconsin bank of the Saint Croix river. 



Figure 3. — Profile along the Minnesota- Wisconsin boundary. 



The profile is taken near the interstate boundary, E i^from Duluth 

 to the Saint Croix river, and G //from the Saint Croix near the 

 mouth of the Kettle river to a point east of Stillwater. The lava 

 flows near the moutli of the Kettle and Snake rivers dip west, and 

 at Saint Croix falls to the southwest, and presumably so at Still- 

 water ; hence the apparent change in dip. 



Figure 4. — Profile across the Keweenawan and associated formations. 



The locality is at Short Line park, in the western part of Duluth, and 

 across the Douglas County fault line. The section in the western 

 part of Duluth is as shown by the boring at Short Line park. 



Figure 5. — Generalized section across the fault line, Douglas Copper range. 



The rocks in their shattered and upturned position prove the up- 

 thrust of the lava flows. 



