264 
IOWA ACADEMY OF SCIENCE 
up the extensive and fertile delta as we find it today. From data 
he has furnished, we learn that the level of the water under the 
bridge, near the buried mill, is 18.6 feet above the ordinary stage 
of the Missouri river west, about 6 feet above the railroad track at 
Bartlett, and 17 feet higher than where it runs under the railroad 
south of Bartlett. The level of the ground is 14.5 feet higher than 
the water, the floor of the bridge is 20 feet higher, and the level 
of an old alluvial terrace near by, probably marking the top of 
deposits antedating the occupation of the lakes by the Missouri, in 
fact recording adjustments long before that, which were similar 
to conditions before the stream broke west in 1875, is 26 feet above 
the water under the bridge or 44 feet above the Missouri three 
miles west, as before. 
It should be stated that the water under the bridge is at present 
(1906) considerably higher than when the Burson mill had 20 feet 
fall, for as the bottom land has been built up in recent years the 
channel of the creek has risen also. Burson thinks the stream is 
nearly up to the level when he had 9 feet fall, and says the piling 
supporting the bridge where the gorge there was the deepest were 
34 feet long, but it is more likely that it is at least 6 feet lower. 
Fluctuations in level of the stream. We therefore see how the 
level of the stream at its debouchure, or egress from the hills, rises 
and falls with different conditions. Its lowest level would be when 
the Missouri comes to that side of its bottom land, when it would 
be nearly the same as the level of the river. Its level would be 
highest when the river is on the west side of its bottoms and the 
junction of the creek with the river very remote, and the whole 
course between built up to its highest grade. Such we may suppose 
to have been the case when the high terrace mentioned was formed. 
Similar histories might be given for every stream entering the 
valley of the Missouri from the hills. North and south of the 
Wabonsie, every valley leading from the hills has a hillock or broad 
low swell of earth on the bottom in front of it. This is true except 
where there is evidence that the Missouri has recently occupied 
the place. The alluvial fans are frequently more abrupt and there- 
fore more marked opposite smaller streams or dry valleys, because 
there has not been water enough to spread the silt. Similar general 
facts have been observed by the writer in northeastern Nebraska. 
Where the alluvial fans have been carried away by the river, there 
are still traces of the fluctuations of level in the valleys back from 
the river. We find flood-plains, sometimes with a fresh-cut ravine 
10-20 feet deep revealing older bottoms with stumps upon them, 
