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Silt
Silt
Fine rock grains between 0.06mm and 0.0002mm across. Silt grains lie between sand and clay in size. Silt grains are easily carried by flowing water.
Silt is only common in rivers in some parts of the world. It is often found in rivers that flow over dry landscapes. Silt makes up nearly two-thirds of the sediment carried by the Mississippi River.
Silt is hard to tell from mud except by feel. Mud is sticky and clings together, but silt is slippery and feels like soap.
The word silt is also commonly used instead of alluvium. However, it is not an accurate use of the word.
Softness
(See: Hardness.)
Spring
A place where water naturally seeps or gushes from the ground.
Springs are fed by groundwater. They occur in aquifers, often where a river cuts down to
the water table. Other springs happen where a permeable rock
is underlaid by an impermeable rock. This sometimes gives rise
to “weeping cliffs,” as water seeps from the base of the permeable rock.
Bubbling or swiftly flowing springs are not especially common. Most rivers begin with muddy patches on a hillside rather than a bubbling spring. Bubbling springs are only possible where the rock below is highly permeable, such as chalk or limestone, or where it is
Spring
Spring
Water table
highly fractured, such as close to a volcano. (See also: Hot spring and Oasis.)
Solvent
A substance in which other materials dissolve. Water is the world’s most common solvent. Even clear tap water, for example, contains a wide range of dissolved minerals, as a glance at the inside of a kettle will show. Some of the minerals are precipitated onto the surface of the kettle as the water is boiled.
 Solvent—Water is an excellent solvent.
This can be seen by evaporating seawater and watching the salts come out of solution to make white rings on the surface of the container.
—Evaporation is complete. Only the dissolved solids remain.
1—Glass bowl containing salty seawater.
2—As evaporation removes water, the water level goes down. A thin film of salt appears on the edge of the bowl.
Sound
(See: Fjord.) 38