View source for Homocline

{{Short description|Geological structure in which rock strata dip uniformly in a single direction}}
{{About|geology|other uses}}
[[File:Rocks near Lulworth Cove.JPG|thumb|Homocline near [[Lulworth Cove]], [[England]]]]
[[File:Thickness.svg|thumb|Diagram of a homocline]]
[[File:Tilted rock strata, Hackley Bay Beach - geograph.org.uk - 375549.jpg|thumb|Homocline in [[Aberdeenshire]], [[Scotland]]]]
In [[structural geology]], a '''homocline''' or '''homoclinal structure''' (from old {{langx|el|homo}}&nbsp;=&nbsp;same, cline&nbsp;=&nbsp;inclination), is a geological structure in which the layers of a sequence of rock [[strata]], either [[sedimentary]] or [[igneous]], [[Strike and dip|dip]] uniformly in a single direction having the same general inclination in terms of direction and angle.<ref name="Jackson2005a">Jackson, JA, J Mehl and K Neuendorf (2005) ''Glossary of Geology.'' American Geological Institute, Alexandria, Virginia. 800 pp. {{ISBN|978-0922152896}}</ref><ref name="Huggett2011a">Huggett, JR (2011) ''Fundamentals of Geomorphology,'' 3rd ed., Routledge, New York. 516 pp. {{ISBN|9780415567756}}</ref> A homocline can be associated with either one limb of a [[Fold (geology)|fold]], the edges of a [[Dome (geology)|dome]], {{clarify span|text=the coast-ward tilted strata underlying a coastal plain|date=August 2022}}, slice of [[thrust fault]], or a tilted [[fault block]]. When the homoclinal strata consists of alternating layers of rock that vary hardness and resistance to [[erosion]], their erosion produces either [[cuesta]]s, [[homoclinal ridge]]s, or [[Hogback (geology)|hogback]]s depending on the angle of dip of the strata.<ref name="Thornbury1954a">Thornbury, W. D., 1954, ''Principles of Geomorphology'' New York, John Wiley & Sons, 618 pp.</ref><ref name="Twidale1993">[[Charles Rowland Twidale|Twidale, C.R.]], and E.M. Campbell (1993) ''Australian Landforms: Structure, Process and Time.'' Gleneagles Publishing, Adelaide, South Australia, Australia. 568 pp. {{ISBN|9781875553020}}</ref><ref name="Gerrand1993a">Gerrard, J (1988) ''Rocks and landforms.'' Allen & Unwin Inc.,Winchester, Mass. 319 pp.  {{ISBN|9780045511129}}</ref> On a [[topographic map]], the landfroms associated with homoclines exhibit nearly parallel elevation contour lines that show a steady change in elevation in a given direction. In the subsurface, they characterize by parallel structural contour lines.<ref name="ReynoldsOthers1993a">Reynolds, SJ, and GH Davis (1996) ''Structural geology of rocks and regions.'' John Wiley, New York, New York. 864 pp. {{ISBN|9780045511129}}</ref>

'''Unicline''' and '''Uniclinal'''  are obsolete and currently uncommon terms that are defined and have been used by [[geologist]]s and [[geomorphologist]]s in an inconsistent and contradictory manner. They are terms that have been used in a mutually exclusive manner as a synonym for either a homocline<ref name="ThomasOthers2000a">Thomas, G, and A Goudie (2000) The Dictionary of Physical Geography, 3rd ed. Blackwell Publishing Ltd., Maiden, Massachusetts. 624 pp. {{ISBN|978-0631204732}}</ref> or [[monocline]]<ref name="U.S.BureauofMines1996a">U.S. Bureau of Mines Staff (1996) ''Dictionary of Mining, Mineral, & Related Terms.'' Report SP-96-1, U.S. Department of Interior, U.S. Bureau of Mines, Washington, D.C.</ref><ref name="NeuendorfOthers2005a">Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, J.A., eds. (2005) ''Glossary of Geology'' (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. {{ISBN|0-922152-76-4}}</ref> depending the author. The meaning of this term has been further confused by Grabau, who redefined ''uniclinal,'' not as a geological structure, but as a general term for ridges produced by erosion of [[anticline]]s.<ref name="Grabau1920a">Grabau, AW (1920a) ''Unicline; a term proposed for monoclinal ridges of erosion.'' Geological Society of America Bulletin. 31(1):153.</ref><ref name="Grabau1920b">Grabau, AW (1920b) ''A Comprehensive Geology, vol. 1'' D. C. Heath & Company, New York, New York. 804 pp.</ref>

The erosion of tilted sequences of either stratified sedimentary or igneous rock, homoclines, of alternating resistance to erosion produce distinctive landforms that form a gradational continuum from cuestas through homoclinal ridges to hogbacks. Less resistant beds are preferentially eroded creating valleys that lie between ridges created by the erosion of more resistant beds. For example, the erosion of homoclines consisting of resistant beds of either limestone, sandstone, or both interbedded with weaker, less resistant beds of either shale, siltstone, marl, or combination of them will produce either cuestas, homoclinal ridges, or hogbacks depending on the angle of dip of the strata.  The greater the difference in the resistance to erosion, the more pronounced the structural control and relief between valley and ridge crest.<ref name="Thornbury1954a"/><ref name="Twidale1993"/><ref name="Gerrand1993a"/>

==Etymology==
According to Whitney in 1890<ref name="Whitney1914a">Whitney, WD (1890) ''The Century Dictionary and Cyclopedia: An Encyclopedia Lexicon of the English Language.'' vol. VI, The Century Company, New York, New York.</ref> and Kelley in 1955,<ref name="Kelley1955a">Kelley VC (1955) [http://cgsdocs.state.co.us/Docs/ERC/MONOCLINES%20OF%20THE%20COLORADO%20PLATEAU-KELLEY%201955a.pdf ''Monoclines of the Colorado Plateau.''] {{Webarchive|url=https://web.archive.org/web/20140222012321/http://cgsdocs.state.co.us/Docs/ERC/MONOCLINES%20OF%20THE%20COLORADO%20PLATEAU-KELLEY%201955a.pdf |date=2014-02-22 }} Geological Society of America Bulletin. 66(7):789-804.</ref> [[Charles Darwin]] used the term ''uniclinal'' prior to 1843 to describe to strata dipping uniformly in one direction. Later in 1843, Rogers and Rogers<ref name="RogersOthers1843a">Rogers, WB, and HD Rogers (1843) ''On the physical structure of the Appalachian chain, as exemplifying the laws which regulated the elevation of great mountain chains generally.'' Association of Geographers and Naturalists. 1:474-531.</ref> created the term ''monocline'' and used it to describe beds dipping uniformly in one direction within the [[Appalachian Mountains]]. However, starting with Powell in 1873,<ref name="Powell1873a">Powell, JW (1873) ''Geological structure of a Grand Canyon of the Colorado.'' American Journal of Science 3rd series, 5(5):456-465.</ref> geologists also used ''monocline'' to specifically describe a step-like fold in otherwise uniformly dipping strata while other geologists still used it to describe beds dipping uniformly in one direction.<ref name="Kelley1955a"/> Thus, the term ''monocline'' was used to describe both beds dipping in one direction and a one-limbed flexure with different authors making incompatible distinctions between them. Because of this confused usage of ''monocline'', Daly<ref name="Daly1915a">Daly, RA (1915) ''A Geological Reconnaissance between Golden and Kamloops, B.C., along the Canadian Pacific Railway.'' memoir no. 68. Canada Geological Survey, Canada department of Mines, Ottawa, Canada. 260 pp.</ref><ref name="Daly1916a">Daly, RA (1916) ''Homocline and Monocline.'' Geological Society of America Bulletin 27:89-92.</ref> formally introduced the term ''homocline'' and in 1915 and 1916 defined it in its current usage and redefined ''monocline'' as a one-limbed flexure as it is currently used.<ref name="Kelley1955a"/>

==References==
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{{Structural geology}}

[[Category:Structural geology]]
[[Category:Geomorphology]]