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No complete topographical survey of the State of Iowa has yet been made. Therefore all the knowledge we have yet upon the subject has been obtained from incidental observations of geological corps, from barometrical observations by authority of the General Government, and leveling done by railroad engineer corps within the State.
Taking into view the facts that the highest point in the State is but a little more than twelve hundred feet above the lowest point, that these two points are nearly three hundred miles apart, and that the whole State is traversed by. . .
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. . . gently flowing rivers, it will be seen that in reality the State of Iowa rests wholly within, and comprises a part of, a vast plain, with no mountain or hill ranges within its borders.
A clearer idea of the great uniformity of the surface of the State may be obtained from a statement of the general slopes in feet per miles, from point to point, in straight lines across it:
| From the N.E. corner to the S.E. corner of the State | 1 foot 1 inch per mile. |
| From the N.E. corner to Spirit Lake | 5 feet 5 inches per mile. |
| From the N.W. corner to Spirit Lake | 5 feet 0 inches per mile. |
| From the N.W. corner to the S.W. corner of the State | 2 feet 0 inches per mile. |
| From the S.W. corner to the highest ridge between the two great rivers (in Ringgold County) | 4 feet 1 inch per mile. |
| From the dividing ridge in the S.E. corner of the State | 5 feet 7 inches per mile. |
| From the highest point in the State (near Spirit Lake) to the lowest point in the State (at the mouth of the Des Moines River) | 4 feet 0 inches per mile |
It will be seen, therefore, that there is a good degree of propriety in regarding the whole State as a part of a great plain, the lowest point of which within the borders, the southeast corner of the State, is only 444 feet above the level of the sea. The average height of the whole State above the level of the sea is not far from eight hundred feet, although it is more than a thousand miles inland from the nearest sea coast. These remarks are, of course, to be understood as applying to the surface of the State as a whole. When we come to consider its surface feature in detail, we find a great diversity of surface by the formation of valleys out of the general level, which have been evolved by the action of streams during the unnumbered years of the terrace epoch.
It is in the northeastern part of the State that the river valleys are deepest; consequently the country there has the greatest diversity of surface, and its physical features are most strongly marked.
