In geology, Smith's laws are two rules, formulated by
William Smith (1769–1839), which aid in the determination of
geological succession. They are fundamental to the production of
geological map
A geologic map or geological map is a special-purpose map made to show various geological features. Rock (geology), Rock units or stratum, geologic strata are shown by color or symbols. Bed (geology), Bedding planes and structural features such ...
s.
The laws
Both laws were first published by Smith in ''Strata Identified by Fossils'', 1816–1819.
Smith's first law
Smith's first law is the Principle of Superposition. This states that newer rock beds will lie on top of older rock beds unless the succession has been overturned. Overturning of the beds causes the succession order to be reversed. This can be caused by
folding
Fold, folding or foldable may refer to:
Arts, entertainment, and media
* ''Fold'' (album), the debut release by Australian rock band Epicure
* Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot
*Abov ...
that is so severe that the beds are moved past the perpendicular. Beds can also be put out of order by an overthrust
thrust fault
A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.
Thrust geometry and nomenclature
Reverse faults
A thrust fault is a type of reverse fault that has a dip of 45 degrees or less.
If ...
(Jackson, p. 128).
Smith's second law
Smith's second law is the Law of Strata identified by fossils. This states that each
stratum
In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...
in the succession contains a distinctive set of fossils. This law allows beds to be identified as belonging to the same stratum even when the
horizon
The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...
between them is not continuous (Jackson, p. 128).
Geological mapping
Smith used these new techniques, together with knowledge he had accumulated as a
canal engineer
A canal engineer is a civil engineer responsible for planning (architectural and otherwise) related to the construction of a canal.
Canal engineers include:
China
* Yu the Great (c.2200BCE-c.2100BCE), first Dynast of China, founder of the fir ...
and
mineral surveyor
Mining in the engineering discipline is the extraction of minerals from underneath, open pit, above or on the ground. Mining engineering is associated with many other disciplines, such as mineral processing, exploration, excavation, geology, and ...
, to produce geological maps. He started with a hand-produced map of the area around
Bath in 1799. In 1815 he published a large-scale map of England, Wales and parts of Scotland. This was the first geological map of Britain (indeed, of any country) and a major milestone in geology (Winchester, p. 195; Jackson, p. 127). In 1819, Smith produced cross-sectional maps showing the underlying geology (Jackson, p. 128).
Smith's map of England and Wales was extensively plagiarised by others, starting with
George Bellas Greenough
George Bellas Greenough FRS FGS (18 January 1778 – 2 April 1855) was a pioneering English geologist. He is best known as a synthesizer of geology rather than as an original researcher.
Trained as a lawyer, he was a talented speaker and his ...
in 1819 (Winchester, pp. 230-234). Smith's laws are still basic to the production of modern geological maps (Jackson, p. 128).
References
Bibliography
* Patrick Wyse Jackson, ''The Chronologers' Quest: The Search for the Age of the Earth'', Cambridge University Press, 2006 .
* Simon Winchester, ''The Map That Changed the World: William Smith and the Birth of Modern Geology'', HarperCollins, 2009 .
* William Smith
''Strata Identified by Organized Fossils'' London: W. Arding, 1816.
{{geology
Geochronology
Geologic maps
Heuristics