192 
The Ohio Naturalist. 
[Vol. VIII, No. 1, 
Aggrading and Degrading. -When the first experiment began, 
the screw was raised about one inch, which gave a slope of one 
inch to thirteen feet, or thirty-four feet per mile, equivalent to 
about one-third of one degree. This is a very steep slope for a 
stream but the smallness of our stream made it necessary, and 
even yet the larger particles of clay were only moved a short 
distance from the heap and that with marked difficulty. Except 
near the clay pile almost no aggrading at all was done. So the 
screw was turned up about one-half inch higher which increased 
the slope to fifty feet per mile. This seems like an enormous 
grade yet the stream still aggraded its lower valley with diffi¬ 
culty. In fact the stream increased its own slope to more than 
two inches in thirteen feet by distributing its sediment thicker 
near the pile of clay. If we could have given the stream more 
time, of course it would ultimately have aggraded its whole 
course without either uplift. 
The supply of clay was repeatedly replenished that the 
stream might be constantly taxed to its utmost, and aggradation 
proceeded. The clay was considerably sorted by the stream. 
With an uniform slope and a shallow stream, as an aggrading 
river must be, the larger particles suffered many halts as they 
were rolled along or dragged on the bottom. While stopped, 
they served as catchers for other particles which would often 
accumulate around them. Most of the larger pieces found per¬ 
manent lodgment before they attained half the journey to the 
lake and hence the delta built during aggradation consisted 
largely of very fine material. 
The group of particles temporarily or permanently retained 
in the channel developed into a sandbar dividing or deflecting 
the water, and causing it constantly to seek new courses. Six 
observations of the stream were made in less than one hour and 
during each interval decided changes occurred. Figs. 3-8. It 
thus appears that a stream engaged primarily in aggrading its 
valley is shallow, constantly filling its own chapnel and breaking 
over its banks. 
Aggradation went on until the upper valley was filled even 
above the rock walls but the lower valley did not fill quite so full. 
In the hope of more nearly filling the lower valley an increasingly 
higher perforated plug was repeatedly substituted for the first 
one, which made the water deeper in the lake. The lower valley 
then filled satisfactorily. 
Upon the completion of the filling process, the heap of clay 
was no longer replenished but other conditions were left un¬ 
changed in order to see whether the stream would cut down into 
its deposits without further change. Erosion began at once and 
the sediments were picked up and pushed or rolled along to the 
lake. Degradation proceeded perceptibly faster in the upper 
