* 
G. K. Warren— Valley of the Minnesota and Mississippi. 429 
ence of many kinds of marine life, and would contain the 
animal remains brought from the fresh-water streams. 
The margins of the loess deposits are not well defined, and do 
not appear to have been investigated as they should be. 
deposit is well shown near Rock Island, but does not appear as 
high up as Dubuque (so farasI know). It extends up the 
Missouri as far as Sioux City, and the Missouri River made 
immense deposits into the body of water in which the loess was 
laid down. From the absence of marine fossils, this body of 
water has been regarded as fresh and without connection with 
the Gulf of Mexico except through an outlet. Judging by 
what I know of the deposits, I should think it did not connect 
with our present Great Lakes, and that a tongue of land or 
promontory separated the arms extending up the Mississippi 
and Missouri Rivers. 
The streams which brought this fine loess material which has 
been so spread out must have brought down heavier material 
along the bottom that fell as soon as it reached the enlarged 
section, just as rivers make their deposits of heavy material 
loess period, and not to glacial times. These deposits are 
where streams would bring them from the northwest, while the 
Cannot be accounted for by any special hardness of the rocks, 
is i d beca 
but their resistance is increase 
*€ 
