late 14c., "vital force in plants and animals;" early 15c., "act of creating or making," from Old French formacion "formation, fashioning, creation" (12c.) or directly from Latin formationem (nominative formatio) "a forming, shaping," noun of action or condition from past-participle stem of formare "to form," from forma "form, shape" (see form (n.)). Meaning that which is formed or created" is from 1640s. In geology, "group of rocks having a similar origin or character," 1815. Related: Formational.
1610s, "gnaw or eat away" (transitive), a back-formation from erosion, or else from French éroder, from Latin erodere "to gnaw away, consume," from assimilated form of ex "away" (see ex-) + rodere "to gnaw" (see rodent). Intransitive sense "become worn away" is by 1905. Related: Eroded; eroding. Originally of acids, ulcers, etc.; geological sense is from 1830.
By CATASTROPHISM I mean any form of geological speculation which, in order to account for the phenomena of geology, supposes the operation of forces different in their nature, or immeasurably different in power, from those which we at present see in action in the universe. [Huxley, "Address" to the Geological Society of London, Feb. 19, 1869]