A cliff-former is a geological unit of bedrock that is more resistant to

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...

than overlying or underlying

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

and consequently produces outcrops with high slope angles. It is more or less equivalent to ''ridge-former'', and may be contrasted with slope-former. In humid environments,

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...

s are typically cliff-formers. In arid environments,

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...

s are often cliff-formers also. Recent

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...

s may be cliff-formers as well. In the Ridge-and-Valley Appalachians of the eastern

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

the major ridge-formers are the

Tuscarora Tuscarora may refer to the following: First nations and Native American people and culture * Tuscarora people **'' Federal Power Commission v. Tuscarora Indian Nation'' (1960) * Tuscarora language, an Iroquoian language of the Tuscarora people * ...

, Pocono, and Pottsville Formations.

References

{{geomorph-stub Erosion landforms Geomorphology