138 Stour City Academy of Science and Letters. 
bottom of every tiny furrow contains a trickling, turbid 
stream; the gullies carry an amount of run-off propor- 
tioned to the area they drain, and, emptying into the 
minor streams, they help swell them into torrents. With 
this movement of water down the slopes soil is cut and 
washed down so rapidly that one can almost see the wast- 
ing of the land. 
That the great rock-bound trough of the Missouri is 
the work of the stream flowing in it is not immediately so 
clear, but given time, that element so potent in geologic 
reasoning, increased velocity due to greater elevation of 
the land, and increased volume and carrying power at 
the time when the ice sheet to the north was melting, and 
the relation of the present river to its valley is no longer 
doubtful. No lake hypothesis is necessary to explain the 
great width of the flat bottom of the valley, and indeed it 
is easily demonstrated by the parallelism in slope of the 
bottom of the trough and the plain above, and their rela- 
tive elevations that no lake could have occupied this 
valley. A study of the other great rivers and their val- 
leys but confirms the idea that this river has excavated 
its trough according to well-known laws of stream 
erosion. 
The elevation of the valley floor above sea level is 
a little over 1,100 feet, the river itself ranging between 
1,076 feet at low water to 1,099 feet at high-water mark 
at Sioux City. The valley floor where widest has a very 
gentle slope laterally to the escarpment of 3 or 4 feet to 
the mile, and the escarpment rises abruptly to a general 
level of nearly 1,400 feet. That the original level has 
already been somewhat lowered is indicated by the fact 
that isolated points attain an elevation of nearly 1,500 
feet, standing perhaps 50 feet above the present general 
level of the divides, but possessing the same character- 
istics of sculpture. 
The smaller tributary streams have not brought their 
valleys down to the level of the main valley floor except 
for a comparatively short distance back from the escarp- 
ment line, their profiles showing still considerably more 
of an inclination than that of the Missouri. 
In some respects, physiographically, the region pre- 
sents the aspect of one that is nearing maturity, and 
some of its characteristics are those of a region that has 
