Soils that have formed in humid areas and are intensely weathered. Contain large areas of clay, and hold most nutrients in only the upper centimeters of this soil. Low fertility.

Dominantly composed of organic matter, often called bogs, peat or muck. Occur in extremely wet areas and have low decomposition rates.

Striking color to layers, these form as rainfall interacts with acidic vegetative litter (usually needles of conifers) to form organic acids, which dissolve minerals. Occur in coarse textured soils in humid areas.

Weathered volcanic ash, resulting in minerals with poor crystal structure. Very fertile but highly erodible.

Soil of tropical or subtropical regions, dominated by iron oxides, quartz and weathered clay. Nearly featureless with no distinct horizons, generally infertile without additives.

Clay rich soils that have a unique quality of expanding and contracting rapidly due to water content. Often form large cracks as they dry and contract, and disrupt structures as they expand when wet. Located in areas where underlying parent materials allow formation of expansive clay minerals.

Occur in climates that are too dry for standard plants to grow in, creating relatively little organic matter. Dry climate also restricts soil weathering processes, and often accumulate salt, gypsum or carbonates.

Form on prairies or grasslands, have a characteristically dark upper horizon, and are highly fertile. Rich in bases such as calcium and magnesium. Often found in climates that have a pronounced dry season.

Similar to ultisols but are less intensively weathered and less acidic. Soil present in much of Pennsylvania. Tend to be relatively fertile and often form under forest vegetation.

Soils that are only just beginning to form, with some horizons but very little clay accumulation. Occur over a wide range of environments and are very common.

Soils that are so new that they exhibit little to no soil development other than a visible topsoil horizon. Often occur in places where deposition of new material is faster than soil development processes, such as floodplains and landslide areas.