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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
of erosion they never extend far back from the Mississippi River. The surface rises 
gradually, however, from the southern and eastern borders toward the northern and 
western, the least elevation above the sea being about 450 feet, and the greatest about 
1,500 feet. Iowa is near the center of the best agricultural portion of the country, 
and the soil, which is from 1 to 2 feet thick on the uplands, becomes very much deeper 
in the depressions and bottom lands. This soil consists of finely comminuted material, 
generally strewn with scattered bowlders or rock fragments. Most of the State is 
undulating or rolling prairie. Rone of its surface is heavily timbered, and the greater 
part of the timber land which does occur is confined to the borders of the streams. 
The prairie was originally covered with a dense growth of prairie grass and her- 
baceous plants, which tended to produce a stiff sod. During heavy rains this sod 
absorbed the water, preventing its direct flow into the rivers, and it reached the latter 
chiefly by slowly filtering through the soil. The streams were thus relieved from over- 
flow, and were kept from drying up during the summers. I have been informed that 
many streams, formerly deep and narrow, and abounding in pickerel, bass, and cat- 
fishes, have since grown wide and shallow, while the volume of water in them varies 
greatly in the different seasons, and they are now inhabited only by bullheads, suck- 
ers, and a few minnows. The breaking of the native sod for agricultural purposes has 
especially affected the smaller streams in this respect, while the construction of ditches 
and the practice of underdraining have had their effects upon the larger ones. More- 
over the constant loosening of the soil, in farming, tends to reduce it to that condition 
in which it is readily transported by the heavy rains to produce muddy currents. To 
this cause, no doubt, is due the present absence of trout from many of the streams of 
northeastern Iowa and their marked decrease in other parts of the State. The rain 
fall in Iowa is not very great and, as it occurs chiefly in the spring, even the larger 
rivers become reduced in volume during the remainder of the year much beyond the 
apparent capacity of their basins. There are, however, in the northern and eastern 
parts of the State many large and beautiful springs, some of which are capable of 
maintaining considerable streams of water during the entire year. Spring Branch, 
near Manchester, in which trout are common, and McCloud Run, near Cedar Rapids, 
are fed by springs of this character. A hatchery was built, a few years ago, at the 
spring giving rise to McCloud Run, and many trout were hatched and planted there. 
This station has recently been abandoned, but a few trout are still to be found in the 
clear, cold water. 
Iowa is situated between two of the largest rivers of the continent, being bounded 
on the east by the Mississippi, and on the west, except at the northwestern corner, by 
the Missouri. It is drained by many smaller rivers which empty into these main 
arteries, forming two general systems, the waters of which flow nearly at right angles 
to each other. Those tributary to the Mississippi trend, in a general way, southeasterly ; 
and those tributary to the Missouri, southwesterly. The northern boundary of the 
State lies near the watershed between the tributaries of the Minnesota River and the 
streams which drain Iowa. Most of the rivers of this State, therefore, have their origin 
within its borders, a few, however, rising in southern Minnesota; and, except a limited 
number whose sources are in the southern part of the State, all terminate within its 
limits. The affluents of the Mississippi drain a little more than two-thirds of the area 
of the State; among them are its largest and most important rivers. 
