88 Tlic American Geologist. February, isos 
lation to the Missouri and Osage rivers shows that it is an out- 
lying remnant of the upland lying between the Osage and 
Missouri rivers. The Osage originally entered the Missouri 
below the lower end of Cote Sans Dessein. Subsequently, by 
the combined sapping of both the Missouri and Osage rivers 
on opposite sides of this upland it was cut through above 
Cote Sans Dessein. At that time or later the Missouri appro- 
priated the lower part of the old Osage valley. Since doing 
this it has doubtless widened this belt so that it is now as 
wide as the old Missouri valley north of the hill. Cote Sans 
Dessein lies directly in the line of prolongation of this upland 
where it still exists. The meander system of both the Osage 
and Missouri rivers shows also that the point where the up- 
land was cut was exposed to the vigorous sapping of both 
streams, being on the convex sides of meanders in both 
streams. Cote Sans Dessein stands where the meandering of 
the Osage at least carried the point of active sapping to the 
southern side of the valley. 
Grand Tower maintains the same relation to the Missis- 
sippi and Big Muddy rivers that Cote Sans Dessein main- 
tains to the Osage and Missouri. It is not so clearly due to 
this relation, however, as is Cote Sans Dessein. There is a 
very great difference in size between the Mississippi and Big 
Muddy. The latter is much smaller than the Osage, but that 
part of the flood-plain lying on the Big Muddy side of Grand 
Tower is much wider than the other. It may be tFue that the 
Mississippi was diverted to the Big Muddy valley soon after 
reaching grade and remained in that position until recently. 
The explanation of its existence is based wholly on its position 
with respect to the two streams. 
The same processes have been operating in at least two 
other places in Missouri. One place is in the vicinity of the 
mouth of Moreau river, which flows into the Missouri about 
four miles above the mouth of the Osage. The Moreau was 
originally tributary to the Osage, entering the latter stream 
near the Missouri Pacific railway bridge. From that point 
up to its present mouth its general course was parallel to that 
of the Missouri, but instead of taking this course in a direct 
line it meandered over a belt more than a mile in width. Its 
own action on the convex side of the meanders combined with 
