GEOLOGICAL REPORT. 
By Epwarp 8. Dana ann Giro. Brrp GRINNELL. 
PRELIMINARY REMARKS ON THE ALLUVIAL DEPOSITS OF THE UPPER MIS- 
SOUR RIVER. 
The town of Carroll is situated in the alluvial bottom of the Missouri, which is at this point 
quite extensive, and well timbered with a fine growth of cottonwood. The course of the river-valley 
is here easterly, and it continues for a considerable distance with but little change in general direc. 
tion, though the valley varies very considerably in width between the high walls of Cretaceous clays 
which rise on either side of it. The river sometimes winds aloug through a bottom two or three 
miles wide, and again is confined to a narrow passage between the steep washed bluffs several 
hundred feet in height. 
The alluvial phenomena are those which are always observed under similar circumstances, though 
they take place here more rapidly and on a larger scale than is often the case, in consequence of the 
vast amount of solid matter which the river is constantly carrying down. On this account, the 
“muddy Missouri” offers peculiar advantages for the study of alluvial changes; and, could a series 
of observations be carried on at a few points during two or three seasons, a large amount of data 
might be collected which would lead to interesting and valuable conclusions. At Carrvll, we have 
an example of a condition of things which may be observed at almost any point in this part of the 
river, and a few words of explanation may consequently not be out of place. At a, on the outer 
bank of the river, the current is strong, and has forced itself 
close up under the high bluffs, whose top forms the border of the 
broad prairie above. The older deposits, at points such as this, 
are directly acted upon by the running water, and are thus grad- 
ually undermined and worn away, the material being carried on by = Z 
%, 
the current. Upon the opposite side of the stream, at c, the current “%, f 
to meet the water in a long low sand-bar. At b, there is a high = 
bank of alluvial clays, 10 feet or more above the stream, deposited ‘ 
jong before in time of flood, but now being rapidly torn away. Still “ 
again at a’ the water washes at the foot of the older bluffs, while 
opposite is the never-failing sand-point. 
Thus the river winds on its course, touching the hills, whichform ss 
the true limit of its valley, only here and there. For the greater t 
part of its course, it is confined between the alluvial banks. It is “% 
safe to say that, except in the epring, the river deposits compara- £ 
tively little solid matter, and this, chiefly on the sand-spits and 2 
bars, where the force of the moving water is small. The work 
of the river is at this season one of destruction more than deposition, tearing down what it has 
13 Ww 
anon, 
anws 
<> 
8S 
8 
ie i 
Sty my, 
=A 
Nr’ 
35) “p i UR 
a ane, Sus aoe 
go : 
iy 
