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Studies for Students.

CONDITIONS OF SEDIMENTARY DEPOSITION.

EROSION.

Erosion consists of fragmental reduction and abrasion of rock masses, chemical disintegration of rocks and transportation. The three sub-processes may be called rock-breaking, rock-decay and transportation. They are conditioned by declivity, lithologic character and climate.

ROCK-BREAKING.

Favorable conditions:

  • (a) Steep slopes.
  • (b) Bare rocks.
  • (c) Cleaved and jointed rocks.
  • (d) Alternation of hard and soft beds.
  • (e) Rapid changes of temperature.
  • (f) Aridity and high winds.
  • (g) Abundant rainfall, in the absence of vegetation.
  • (h) Sea cliffs.

Products: Shingle, gravel and sand of mixed mineralogical composition.

ROCK-DECAY.

Favorable conditions:

  • (a) Gentle slopes.
  • (b) Porous soil.
  • (c) Soluble rock constituents.
  • (d) Carbonic acid and other acids of organic decay.
  • (e) Abundant rainfall in the presence of vegetation.
  • (f) Prolonged transportation of gravel and sand.

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