Clay, Sand, and Loam - Soil Types in Geology answers questions

Soil Types

Soil types
Soil Types Triangle

All dirt is basically made of three different kinds of particles. These are clay, sand, and loam. Clay is very fine, small inorganic particles, worn down from rock. Sand is bigger, coarser particles, also from rock, often quartz or silica. Loam is organic particles (bits of dead plants). Geologists and archaeologists can describe any particular soil by saying where it lies in this triangle.

The best soils for farming have a lot of loam in them; they fall near the top of the triangle, like the blue spot. Down where the purple spot is, that would be good clay for making pottery. Over by the green dot, that's sand that you can melt down into glass. The orange dot marks a good soil with a lot of loam in it, , but it does have a lot of clay in it, and that makes it heavy and hard to plow.

You need animals to pull the plow. A lot of northern European soils are like that, and also the soil in river valleys like the Nile. The yellow dot marks soils that are more typically Mediterranean: a mixture of loam and sand, with only a little clay, light enough to plow by hand.

Learn by doing: check out the dirt in your yard or a park. Is it sandy? Clay? Loam?
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Bibliography and further reading about soil types in archaeology:

Archaeology : Uncovering the Mysteries of Our Past, by Richard Panchyk (2001). With twenty-five projects, like counting tree rings, and serializing cars from photographs. Includes a project on soil types.

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Professor Carr

Karen Eva Carr, PhD.
Assoc. Professor Emerita, History
Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

Professor Carr's PSU page

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