326 C. W. HALL — KEWEENAWAN AREA OF EASTERN MINNESOTA 



was a controlling factor in holding down to a minimum the erosion of 

 the Keweenawan at this place. The amount is much less than that 

 along the Snake river at Chengwatana. 



Just below the Big rapids is a conglomerate bed 100 feet in thickness. 

 It lies conformably with the lava flows. An average of several measure- 

 ments gives strike south 10 degrees west, dip 132 degrees west. The 

 varying hardness of this bed forms a succession of reefs across the river, 

 while its readier disappearance under erosion, as com})ared with the 

 more crj^stalline lava flows, is the probable cause of the rapid cutting 

 into the eruptives immediately above. There are quite diverse textural 

 characters in the beds ; some laj'-ers are of normal sandstone, while 

 others are made up of pebbles of large size. Quartzite, quartz por- 

 phyr}^ felsite, red granite or augite syenite, gray granite, dialxase, and 

 diabase pori)hyry are among the rock species represented by these well 

 worn fragments. Underlying this conglomerate are more lava flows in 

 normal succession. 



Continuing down the stream three other conglomerate l)eds are passed 

 ])0ssessing the same general characters as the one below Big rapids. 



A conglomerate of considerable extent lies in section 29 of this town- 

 ship. Its strike varies from north to south to south 10 degrees west, 

 dipping westerl}' at angles var3'ing between 8 and 15 degrees. Its frag- 

 ments vary from ordinary sand grains to good sized boulders. Its 

 thickness is estimated at 50 feet, and it is separated from the bed below 

 the Big raj)ids just described by possibly two or three lava flows. 



In section 32, township 40, range 19 west, a thin bed of conglomerate 

 overlies an extensive bed of tuff". The color of this, as of the other clastic 

 beds, is red, and the fragments making up the material of all the mem- 

 bers of the series show an intimate relationship of the series from the 

 lowest to the highest. 



In section 8, townshij) 39, range 19 west, lies the last and lowest con- 

 glomerate bed of the Kettle River exposures. Its thickness is estimated 

 at 50 feet. It is more arenaceous than either of the beds already men- 

 tioned. In strike it bears more westerly than the others. 



The lava flows which lie here alternating with the conglomerates just 

 located possess strikingly similar characters. The compact lower and 

 middle portions of each are followed by the amygdaloid. In one place, 

 however, is an interesting variation from the standard type. Along a 

 considerable part of section 32, township 40, range 19 west, lies a bed of 

 tuff*. The rock is so decomposed that specimens can scarcely be broken. 

 Rather frequent calcite-filled cavities and veins occur. Crystalline laj'ers 

 are associated with others so soft and decomposed that specimens cannot 

 be dressed from them. It may be mentioned in passing that this tuff 



