PETROGRAPHY OF THE KEWEENAW AN 637 



develop locally; e.g., a banding simulating gneissic structure in a 

 flow on Snake River, and a schistose streak a few inches wide in a 

 flow seen by Berkey at Taylors Falls. 



Near the fault the strike of the flows follows the fault quite closely. 

 The general structure is a qomplex syncline. Beginning at the south, 

 it is clear that the axis of the syncline must pass between the Taylors 

 Falls rocks, dipping 15 degrees south, 70 degrees west, and the Snake 

 River series, dipping 70 degrees south, 80 degrees east. . On Kettle 

 River the axis of the syncline is located within a few hundred paces. 

 The flows farthest up the river, near the fault, dip 50 degrees south, 

 70 degrees east, and near the mouth other flows dip 20 degrees 

 north, 70 degrees west. Near Kettle River the strike changes rather 

 abruptly, swinging more easterly as one follows a flow northward. 

 In this northeastern area no dip of more than 45 degrees was observed 

 and no outcrop was found southeast of the synclinal axis. Some 

 observations, however, indicate the proximity of the axis. In 

 Wisconsin the axis was sketched by the early geologists,' running 

 southwest close to the St. Croix, for a long distance, always on the 

 Wisconsin side. To connect their observations with those on Kettle 

 River requires a double curve in the axis, crossing the St. Croix near 

 the mouth of Tamarack Creek. An alternative might be the sugges- 

 tion that the sharp fold on Snake River, which becomes less sharp on 

 Kettle River and stifl less on the next stream, gradually disappears to 

 the northeast; and the whole may be a secondary fold in the north- 

 west limb of the main Keweenawan syncline, which would then be 

 nearly as Irving sketched it. No correlation of beds across the syn- 

 cline has been possible. In the clear exposures of Kettle River 

 series, several conglomerates are seen on the southeast and none on 

 the northwest, but this may be an accidental disagreement in an 

 incomplete series, because conglomerates are known on Snake River, 

 west of the syncline. 



Areal. — The map (Fig. i) shows the general region of outcrops. 

 The three main types of lava distinguished in this paper are widely 

 distributed and it cannot be said that any one of them is absent in 

 any of the extensive series. Exposures are hardly clear enough to 

 note any change in the general character from the earliest to the 

 I U.S.G.S. Mon. V. 



