Soils Display for Smithsonian

Information Sheet

About Soil Monoliths
Soil monoliths are soil profiles that have been mounted on a board, making it possible to “transport” the natural soil and display it at remote locations.  Soil monoliths are an important tool for observing soil profiles and comparing different soil types.  It is easier to understand and appreciate soil characteristics and properties when observed and compared side by side.

A representative soil is selected at a field location and a pit is excavated to expose the soil profile.  The soil monolith is then prepared by extracting the soil profile and gluing it to a board.  The soil is allowed to dry and then saturated with a fixative that permanently binds the soil.  Additional treatments are made to the monolith to preserve the natural appearance of the soil profile.

About Soil Series and Profiles 
A group of soils having similar properties and behavior characteristics is called a series.  Each series consists of soils having major horizons, or layers, which are similar in color, texture, structure, reaction, consistence, mineral and chemical composition, and arrangement in the soil profile.  The United States has more than 20,000 different soil series.  A series name is generally derived from a town or landmark in or near the area where the series was first recognized.

A soil profile is the sequence of natural layers, or horizons, in a soil.  It extends from the surface downward to the unconsolidated material in which the soil formed.  Most soils have three major horizons called the surface layer, the subsoil, and the substratum.

The surface layer has the maximum accumulation of organic matter and is the layer of maximum leaching of clay minerals and of iron and aluminum oxides.  Some soils have a subsurface layer below the surface layer.

The subsoil, which underlies the surface or subsurface layer, is the layer of maximum accumulation of clay minerals, iron and aluminum oxides, and other compounds.  These may have been leached from the surface layer or may have formed in place.  The subsoil commonly has blocky structure and generally is firmer and lighter in color than the surface layer.

The substratum is below the surface layer and subsoil.  It consists of material that has been modified by weathering but is relatively unchanged by soil-forming processes.

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