46 The American Geologist. juiy, i89i 
was oompletel}- filled with earth, thus burying the house aud 
all. All these mounds show the hearth as a burned cla}' bottom 
with charcoal and ashes. The terrace-mounds were built when 
the flood-plain was covered with water and when the lake reached 
the base of the blutfs. The mounds on the bluffs were generallj- 
loose piles of stones having circular openings or hollow cones 
high enough for a man to stand erect. The}' ma}' have been look- 
outs or war towers. The lowas and the Omahas came here after 
the expulsion of the Assiniboines. They had villages at Lake 
Pepin. There are mounds at Lake City which are said to have 
been built by the Omahas. There are game drives. The Oma- 
has were driven out of the state by Red Wing and by Wabasha. 
There are large mounds at Belle Creek in the shape of effigies on 
an isolated knob, one in the shape of a turtle. " 
The writer has discovered the same succession of mounds in 
Wisconsin and other places. Here the latest were nearest the 
water, those earlier were on the terrace above and the earliest of 
all on the top of the bluffs. These were effigies. The mound 
builders proper were in the country when the flood-plains were too 
wet to admit of access. But the Indians came and encamped on 
these flood-plains, leaving shells and hearths andadebris near the 
water after the water had subsided. A succession of mound 
builders filling up the gaps and making the terraces the places 
where they built their mounds. 
Here, then, we have the same story as before ; some of the 
mounds wei-e built since the flood-pjain was dry, or comparativel}- 
so, these being cotemporaneous with the later Indians, and some 
of them built when the water was over the terraces and near the 
bluffs, evidently l)uilt by the earlier mound builders. 
Let us go down the river farther and look at another class of 
works. We find a flood-plain but it seems old, and the works on 
it even older than the plain itself. We can imagine how the hunter 
kept out of the way of the flood and yet built his burial-mounds 
on the bluffs adjoining the swamps and lakes. But what shall we 
say about the agriculturist who built his pyramid on the flood- 
plain itself ? Here is the Cahokia mound; it is 100 feet high, 
has a terrace 300 feet wide, and fifty deep. It is attended by 
sixty or seventy other mounds similar in shape and size. These 
mounds are all on the great American bottom; that bottom is a 
flood-plain ; it is a flood-plain which is now rarely overflowed. The 
