370 The American Geologist. June, i9oo 
whole country and forming the characteristic soil of northern 
Missouri. It has been cut through along the valleys and in 
places on the steeper slopes, but enough remains to demon- 
strate its original continuity over all the country between the 
Iowa line and the Missouri and Mississippi rivers. The most 
remarkable feature of it is its comparative uniformity of thick- 
ness. True, it thickens in the valleys and thins over the di- 
vides, but there is no observable tendency in it to fill any of the 
old pre-Iowan valleys, except within thirty miles of the Mis- 
souri river, where the clayey silt thickens to a great rolling 
sheet which almost completely obscures the drift and solid 
rock formations. The uneven surface of this broad belt of 
distinctly Missouri river loess is partly the result of erosion, 
but largely original. For instance, at Boonville we find the 
high hills, rising 150 or more feet above the Alissouri river, 
heavily covered with loess so that the underlying rock is 
rarely exposed even in ravines. On the south is a broad, deep 
valley whose floor and slopes are lined with the same sheet of 
loess. It is preposterous (in the light of post-Iowan erosion 
as recognized in other districts) to suppose that these deep val- 
leys were silted up to the level of the uplands, and their pres- 
ent existence be due to post-Iowan erosion. All over north- 
ern Missouri the same line of evidence leads to the same con- 
clusion, namely, that the whole body of the loess when com- 
pleted had almost as uneven a surface as at present. This ef- 
fectually disposes of the fluvial theory, for it is not known to 
be the habit of rivers to wander about over a hilly country 
and finally leave it almost as undulating as at first. 
It is claimed by the supporters of the fluvial hypothesis, 
that a barrier existed across the courses of the Missouri and 
Mississippi rivers, holding the water level up to the level of 
the present uplands, then a plain, upon which the loess was 
deposited; subsequently, the valleys were eroded, and the loess 
at present on 'their slopes and bottoms is due to slow "creep- 
ing" from the uplands. Both these positions are untenable. 
First, the valleys of northern Missouri were cut down nearly 
to their present level before the loess was deposited. This is 
proven by their large size, and by the existence of a weathered 
layer and soil at the surface of the drift and under the loess 
throughout the valleys except where recent erosion has de- 
