330 C. W. HALL — KEWEENAWAN ARE^A OF EASTERN MINNESOTA 



thinner bed of this same clastic material is reached. This is identical in 

 petrographic characters with the four preceding beds. 



ATTITUDE OF THE SERIES 



The attitude of all these conglomerate beds is substantially the same, 

 and identical with that of the diabase flows, the strike being north 10 

 degrees east and dip east 67 degrees. Here and there are indications of 

 slight movement, as slickensides and fractures; a few occurrences of a 

 thoroughly fractured condition of the rocks is noticeable, but nowhere 

 is a fault line seen. The inference is clear that the rocks from one end 

 of the section to the other are continuous and represent a vast succes- 

 sion of flows and clastic beds lying one on tVie other without a break. 



THE LIMITS OF THE SERIES 



It'must be assumed that the lava flows at the dam, while not deter- 

 mined to be lowest, are among the bottom flows of the series. There is 

 an absence of any surface features north or south suggestive of changed 

 rock conditions; yet it must be concluded that the fault plane which 

 the artesian well 1} miles away l)rings into such strong probability is 

 quite near the dam. 



It is no easier to assume the eastern limit or top of the series. The 

 easternmost exposure is said by Mr J. F. Stone to be near the mouth of 

 a small creek entering the Snake in the southwest quarter of section 19, 1\ 

 miles across the strike from the lowermost flow in sight at Chengwatana. 

 The dip at this point is said to be the same as at })oints well exposed — 

 that is, around 67 degrees east ; yet if the lava flows ex})osed on the 

 Kettle river be projected across the intervening country to the Snake 

 river, the strike of the uppermost flow seen on the former stream will 

 cross the latter near the middle of section 28, or 21 miles due east of 

 the exposure in section 19, just mentioned. Thus a total distance of 41 

 miles is secured-as the breadth of the western side of the great syncline 

 which stretches from Keweenaw point southwestward beyond Stillwater, 

 Minnesota. 



THICKNESS OF THE CHENGWATANA SERIES 



The total thickness of the 65 lava flows measured and their associated 

 conglomerate beds is over 4,000 feet (see plate 27, figure 2). This is not all 

 the series ; the distance across the strike to the point in section 19 where 

 the rocks are last seen is 2} miles ; at the same eastward dip, as was meas- 

 ured on the rocks in sight, the total thickness to this point is 10,940 feet ; 

 yet the exposure in section 19 is only one-half the distance to the line 



