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It will be seen that all the stratified rocks of this region may be referred to five of the principal systems of geologists, as follows:

• Quaternary,
• Tertiary,
• Cretaceous,
• Carboniferous,
• and Lower Silurian.

Each of these will now be described separately.

QUATERNARY DEPOSITS.

The Quaternary System comprises all the deposits of later date than the Tertiary, and in descending order includes:

• 1st, Alluvium;
• 2d, Bluff Formation or Loess;
• and. 3d, Drift or Boulder Formation.

Their aggregate thickness in the district under consideration has been estimated approximately at about six hundred feet.

ALLUVIUM.

This formation comprises:

• 1st, Soils;
• 2d, Sand and Pebbles;
• 3d, Clays;
• 4th, Stalactites;
• and, 5th, Calcareous Tufa.

SOILS.

When we consider the extent of surface and variable geological composition of this district, it is not surprising that we should find within its limits a great variety of soils. These, it is well known, derive their character mainly from the mineralogical composition of the underlying strata; and in proportion as these abound in materials favorable or unfavorable for the nutrition of plants, will the soil, other things being equal, be productive or unproductive.

Many of the soils encountered upon the Plains are found to possess in an eminent degree all the necessary elements of nutrition for plants, and if this region were accompanied with the requisite meteorological conditions it would possess a character for fertility unsurpassed by any portion of the North American continent.

Marly Clay Soil.-The most extensive and under favoring circumstances the most productive variety of soil is that derived from the Marly Clay Formation, which is spread over thousands of square miles of surface. It is for the most part of a deep red or brown color, and contains silica, carbonate and sulphate of lime, allumina, magnesia, and oxide of iron, in variable proportions. Could any means be adopted for transporting it to market it would be highly valuable as a manure. Along the streams and in other moist situations it is generally thickly covered with vegetation.

Gypsum Soils.-Gypsum enters largely into the composition of many of the soils of the Plains, and often in such quantities as to constitute their most abundant ingredient. These soils are sometimes white, but more frequently of a light grey, bluish, or red color. They are usually very light,