Siltstone
Lithified sediment chiefly composed of silt-sized particles, generally finer than sandstone and coarser than claystone.
Language and route: English silt + stone; silt is an inherited sediment word whose quantitative grade was standardised much later. English silt + stone; silt is an inherited sediment word whose quantitative grade was standardised much later
Literal gloss: rock of silt
The name and its history
First geological naming act not verified · First geological printed use not verified
- What does the word literally mean?
- Immediate borrowing/formation pathway: English silt + stone; silt is an inherited sediment word whose quantitative grade was standardised much later. Linguistic gloss: ‘rock of silt’. This is not automatically the original namer’s stated reason.
- What did the original author mean?
- Silt was described in rivers and fine deposits before the twentieth-century sediment-grade schemes supplied common numerical boundaries. Lithified silt needed identification independently of weathering colour or clay-like field behaviour.
- Why was the name needed?
- Naming the interval between sand and clay enables reproducible mapping and comparison of environments that deposit otherwise indistinguishable fine sediment.
- What evidence supported the original concept?
- Particle size, gritty feel where detectable, thin-section/sediment analyses and bedding; Wentworth’s 1922 grade scale marks standardisation, not a first use of the word.
- How has geology changed the concept?
- The clay/silt boundary is not identical in all national classification protocols; USGS stresses silt dominance and lack of conspicuous shale fissility.
Further historical context
Silt was described in rivers and fine deposits before the twentieth-century sediment-grade schemes supplied common numerical boundaries. Lithified silt needed identification independently of weathering colour or clay-like field behaviour.
Naming the interval between sand and clay enables reproducible mapping and comparison of environments that deposit otherwise indistinguishable fine sediment.
Particle size, gritty feel where detectable, thin-section/sediment analyses and bedding; Wentworth’s 1922 grade scale marks standardisation, not a first use of the word.
The clay/silt boundary is not identical in all national classification protocols; USGS stresses silt dominance and lack of conspicuous shale fissility.
Editorial qualification
First coinage/priority not independently established; historical narrative is a source-bounded reconstruction.
Related names
Sources
- British Geological Survey, Rock Classification Scheme, Volume 3 overview — Modern descriptive sedimentary classification; does not establish historical first use
- USGS, Lithologic classification of geologic map units — Alternative modern operational vocabulary, including mudrocks
- USGS thesaurus: Siltstone — Silt predominance and fissility
- Wentworth (1922), A Scale of Grade and Class Terms for Clastic Sediments — Original 1922 classification paper, verified title/DOI and journal pagination; full article not transcribed