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Webster 1913 Edition

Noun.

[Cf. Norw.

gald

hard ground, Icel.

gald

hard snow.]

(Geol.)

A series of beds of clay and marl in the South of England, between the upper and lower greensand of the Cretaceous period.

gault ‎(countable and uncountable, plural gaults)

A type of stiff, blue clay, sometimes used for making bricks.
- 1901, Charles Kingsley, Two Years Ago, Volume I:
  As he spoke, they turned off the main line of the rolling clays toward the foot of the chalk hills, and began to brush through short cuttings of blue gault and "green sand," so called by geologists, because its usual colours are bright brown, snow-white, and crimson.

type of stiff, blue clay