Who IS Smith, William H. (1769–1839) British Geologist

William Smith was born in Churchill, Oxfordshire, where he became

an apprentice surveyor. His experience outdoors led him to

become interested in the rocks he was surveying, and he

began surveying the coalfields in Somerset and then had the

opportunity to survey a canal construction project, where he

completed detailed geological investigations on the rocks the

canal was being cut through. During this study, he mapped

different sedimentary facies in the rocks and collected fossils

and identified specific fossils assemblages in rocks of certain

ages, in different facies. By this study, he proposed in 1796

that some strata could be identified by specific index fossils

they contained, without regard to the rock type. He continued

to travel and map different rock units around the United

Kingdom for many years, and in 1801 Smith completed a

simple geological map of England and Wales. For the next 10

years, William Smith worked incessantly on improving his

maps, and in 1815 he produced the first detailed geologic

map of England and Wales, showing more than 20 different

units, topography, and description of the stratigraphy, and

structural cross sections. During the same time, Smith produced

his works on “Strata Identified by Organic Remains,”

in which he illustrated the fossils in the rocks through a series

of wood engravings. In 1831 the Geological Society of London

awarded William Smith the first Wollaston Medal, its

highest honor. Since his death, William Smith has been

known as the “Father of English Geology.”

snow See PRECIPITATION.

soils All the unconsolidated material resting above

bedrock. Soils are the natural medium for plant growth. Differences

in soil profile and type of soil result from differences

in climate, the rock type it started from, the types of vegetation

and organisms, topography and time. Normal weathering

produces a characteristic soil profile, marked by a

succession of distinctive horizons in a soil from the surface

downward. The A-Horizon is closest to the surface and usually

has a gray or black color because of high concentrations

of humus (decomposed plant and animal tissues). The AHorizon

has typically lost some substances through downward

leaching. The B-Horizon is commonly brown or

reddish, enriched in clay produced in place and transported

downward from the A-horizon. The C-Horizon of a typical

soil consists of slightly weathered parent material. Young

soils regularly lack a B-horizon, and the B-horizon grows in

thickness with increasing age.

Some unique soils form under unusual climate conditions.

Polar climates are typically cold and dry, and the soils

produced in polar regions are typically well-drained without

an A-horizon, sometimes underlying layers of frost-heaved

stones. In wetter polar climates, tundra may overlie permafrost,

which prevents the downward draining of water.

These soils are saturated in water and rich in organic matter.

These polar soils are very important for the global environment

and global warming. They have so much organic material

in them that is effectively isolated from the atmosphere

that they may be thought of as locking up much of the carbon

dioxide on the planet. Cutting down of northern forests

as is occurring in Siberia may affect the global carbon dioxide

budget, possibly contributing to climate change and

global warming.

Dry climates limit the leaching of unstable minerals such

as carbonate from the A-horizon, which may also be

enhanced by evaporation of groundwater. Extensive evaporation

of groundwater over prolonged times leads to the formation

of caliche crusts. These are hard, generally white

carbonate minerals and salts that were dissolved in the

groundwater but were precipitated when the groundwater

moved up through the surface and evaporated, leaving the

initially dissolved minerals behind.

In warm, wet climates, most elements (except for aluminum

and iron) are leached from the soil profile, forming

laterite and bauxite. Laterites are typically deep red in color

and are found in many tropical regions. Some of these soils

are so hard that they are used for bricks.

Soils form at various rates in different climates and other

conditions, ranging from about 50 years in moderate temperatures

and wet climates to about 10,000 to 100,000 years for

a good soil profile to develop in dry climates such as the

desert southwest of the United States. Some soils, such as

those in the tropics, have been forming for several million

years and are quite mature. Deforestation causes erosion of

soils, which cannot be reproduced quickly. In many places,

such as parts of Madagascar, South America, and Indonesia,

deforestation has led to accelerated rates of soil erosion,

removing thick soils that have been forming for millions of

years. These soils supported a rich diversity of life and it is

unlikely that the soils will ever be restored in these regions.

See also MASS WASTING; WEATHERING.

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