The State of Illinois forms the lower part of that slope which embraces the greater part of Indiana, and of which Lake Michigan, with its shores, forms the upper part.  At the lowest part of this slope, and of the State, is the city of Cairo, situated about 350 feet above the level of the Gulf of Mexico, at the confluence of the Ohio and the Mississippi; hence, the highest place in Illinois being only 800 feet above the level of the sea, it will appear that the whole State, though containing several hilly sections, is a pretty level plain, being, with the exception of Delaware and Louisiana, the flattest country in the Union.

The State contains about twenty-five considerable streams, and brooks and rivulets innumerable.  There are no large lakes within its borders, though it has some sixty miles of Lake Michigan for its boundary on the east.  Small clear lakes and ponds abound, particularly in the northern portion of the State.

As to the quality of the soil, Illinois is divided as follows:—­

First, the alluvial land on the margins of the rivers, and extending back from half a mile to six or eight miles.  This soil is of extraordinary fertility, and, wherever it is elevated, makes the best farming land in the State.  Where it is low, and exposed to inundations, it is very unsafe to attempt its cultivation.  The most extensive tract of this kind is the so-called American Bottom, which received this name when it was the western boundary of the United States.  It extends from the junction of the Kaskaskia and Mississippi, along the latter, to the mouth of the Missouri, containing about 288,000 acres.

Secondly, the table-land, fifty to a hundred feet higher than the alluvial; it consists principally of prairies, which, according to their respectively higher or lower situations, are either dry or marshy.

Thirdly, the hilly sections of the State, which, consisting alternately of wood and prairie, are not, on the whole, as fertile as either the alluvial or the table-land.

There are no mountains in Illinois; but in the southern as well as the northern part, there are a few hills.  Near the banks of the principal rivers the ground is elevated into bluffs, on which may be still found the traces left by water, which was evidently once much higher than it now is; whence it is inferred, that, where the fertile plains of Illinois now extend, there must once have been a vast sheet of water, the mud deposited by which formed the soil, thus accounting for the great fertility of the prairies.

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