Xof(\^ on the Local Geolofftj of Manhito - Bechdolt. r»9 



to become a stream again near fciie city limits and flows into the 

 Minnesota river at Mankato. Drift material is spread upon the 

 sides of this valley and at several places terraces are clearly marked. 

 This therefore must be regarded as a valley made in pre- 

 glacial times and re-opened at the close of the Ice age. No ter- 

 races can be seen along the Le Sueur below the point where this 

 depression opens into the valley of this river or along the Blue 

 Eartli I'iver north of their union. From above the dam at the 

 Red Jacket Mill to the river, just below the mill, the w^ater falls 

 eleven feet, and there is a marked fall in the Le Sueur below this 

 point to where the Le Sueur and Blue Enrth rivers join. I deem it 

 therefore safe to estimate the fall in the Le Sueur from Chalk run 

 to its mouth at fifteen Jeet. Where the Slough and the Blue 

 Earth valley make the closest approach there is a ridge of sand and 

 gravel, modified drift in fact. This ridge is lower than those on 

 either side which are underlaid by the Shakopee and Jordan for- 

 mations. Man has taken advantage of this low saidy ridge to 

 carry the wagon and railroad from the Slough valley over to that 

 of the Le Sueur river. From the facts here stated we conclude 

 that the Slough valley marks a former channel of the Le Sueur 

 and Blue Earth rivers; that these rivers united north of Indian 

 Lake: that the Blue Earth river changed its course because of the 

 ridge of modified drift extending across it near the junction, and 

 by uniting more recently with the Le Sneur river at lied Jacket 

 Mills left the valley of the Slough dry throughout its length, ex- 

 cept where the retiring w^ater left a pool, at Indian Lake, to mark 

 the deepest places in the channel. Xw inspection of the locality 

 will show even better than a chart, that at a time when the Le 

 Sueur yet held its course along the Slough, the Blue Earth w-ound 

 in a sharp curve round by Red Jacket Mill, leaving the knoll near 

 the mill, now surrounded by meadows, as a bench or terrnce on 

 its northern bank. The two rivers were then separated l)y a nar- 

 row ridge underlaid by friable Jordan sandstone, tangent to the 

 wearing side of the channel of both rivers. A gully, such as exists 

 on the south bank today and is used by the railroad, may have 

 materially lessened the distance. Sometime when the Le Sueur 

 was gorged with ice it broke down the wall and left its old and 

 tortuous course by the slough for a channel more direct and 

 steeper. 



A similar chan^o has come about in the Blue Earth river 



