Valley
Collier's New Encyclopedia (1921)
in geology, a long depression or hollow on the surface of the earth, margined by ground more or less high. It may be on a vast scale of magnitude, as the bed of an ocean would be if upheaved sufficiently to become land, or it may be comparatively small but broad; or narrow, as a glen or a deep gorge, called by Americans a cañon or gulch. It may be surrounded by hills, or may constitute a depression crossing a country from sea to sea. Valleys of stratification are produced by the decay and removal of shale or other soft rocks, while the less destructible hard rocks remain. Other valleys have been excavated by rivers alone. Many valleys on low-lying plains adjacent to the sea have originally constituted river beds and banks, then through a depression of the land the ocean has gained access to them, constituting them estuaries; then again upheaval has made them land valleys. Other valleys have constituted the beds of old lakes. Valleys, resembling troughs, on table-lands are in many cases produced by the flexure of strata laterally, so as to constitute a series of elevations and depressions. A small number of valleys occurring high up mountain sides may constitute old craters of eruption. In anatomy, a deep fossa separating the hemispheres of the cerebellum (called also vallecula). In architecture, the internal angle formed by the junction of two inclined sides of a roof. lines; but, as he was not very cordially harnois co., Quebec, Canada; on the St.
What Has Changed in the Last Century
Collier's 1921 list of valley types — stratification, river cutting, drowned estuaries, old lake beds, lateral flexure of strata — is still a fair description of what valleys look like, but the deepest cause was missing. Plate tectonics, accepted in the 1960s, explained the great rift valleys of East Africa and the Rhine as products of crustal extension, and echo‑sounding surveys led by Bruce Heezen and Marie Tharp in the 1950s found a continuous rift valley running down the crest of the mid‑ocean ridge, on the sea floor the 1921 writer could only imagine upheaved into land. Two other kinds of valley have since been added: J Harlen Bretz's argument that the Washington coulees were gouged in days by catastrophic glacial‑lake floods, ridiculed in the 1920s and vindicated by the 1960s and 70s, and the drowned valleys behind twentieth‑century dams. The anatomical vallecula and the architectural roof valley are unchanged usages.
Written for this edition, 2026.