<descriptor thcode="2"><thesaurus thcode="2" name="USGS Thesaurus" scope="Topics and methods of scientific study carried out by USGS, with product types, scientific disciplines, geologic time, and types of institutional structure and activities.  Broad and shallow, used to help people find scientific information." creator="U.S. Geological Survey" rights="Public domain" edition="2.0" date="2020-01-09" codetype="number" prefix="topic" uri="https://www2.usgs.gov/science/USGSThesaurus" tblname="term" nonpref="nonpref" relterm="relterm" root_code="1" contact="pschweitzer"><category><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/><term thcode="25" code="29" name="distinct labels" parent="26" scope="Preferred labels (descriptor texts) are distinct within the thesaurus. A concept can be specified either by its unique identifier (code) or by the text of its descriptor."/><term thcode="25" code="16" name="hierarchical" parent="11" scope="Substantive broader-narrower relationships exist among the terms."/><term thcode="25" code="13" name="transitive" parent="12" scope="Narrower terms have an &quot;is a&quot; relationship with their broader terms, and generally can be described as part-of, type-of, or instance-of the broader term."/><term thcode="25" code="21" name="disciplines" parent="2" scope="Broad categories of human inquiry or activity, such as scientific disciplines."/><term thcode="25" code="20" name="methods" parent="2" scope="Actions taken to obtain or analyze information"/><term thcode="25" code="19" name="organizational functions" parent="2" scope="Things that organizations do, typically including various types of programs, projects, and services."/><term thcode="25" code="7" name="temporal" parent="2" scope="Terms indicate periods of time, such as chronostratigraphic units, named historical periods or intervals surrounding known historical events, or seasons."/><term thcode="25" code="5" name="theme" parent="2" scope="Terms indicate domains of human concern, such as scientific discipline, societal problems, or characteristics of earth, space, oceans, and living things."/></category><altlabel><altlabel>USGSThesaurus</altlabel><altlabel>USGSThesaurus</altlabel></altlabel></thesaurus><term thcode="2" code="1037" name="sedimentology" parent="464" scope="Branch of earth sciences concerned with the study of the origin, composition, transport, and changes of materials deposited by water, wind, or ice."/><bt><term thcode="2" code="464" name="geology" parent="291" scope="Study of the planet earth, its composition, structure, physical and chemical processes, and history since its origin."/><term thcode="2" code="291" name="earth sciences" parent="1019" scope="Broad term for all science related to the study of the earth."/><term thcode="2" code="1019" name="sciences" parent="1" scope="Major educational fields, fields of study, and professional groupings within USGS."/><term thcode="2" code="1" name="Categories" scope="Thematic terms for categorizing information resources.  This thesaurus is intended to support finding and understanding scientific information."/></bt><rt><term thcode="2" code="83" name="bedforms" parent="1035" scope="Fluctuations from horizontal layers in sediments or sedimentary rocks made by flow on the beds of alluvial channels."/><term thcode="2" code="132" name="building stone resources" parent="798" scope="Deposits of rocks used in construction, including crushed stone and dimension stone. Dimension stone includes limestone and granite, quarried in large blocks, and shaped in cubes, panels and other forms."/><term thcode="2" code="164" name="clay deposits" parent="1199" scope="Fine-grained sedimentary soil deposits, containing hydrated silicas of aluminum, that are plastic and sticky when wet and harden when heated."/><term thcode="2" code="248" name="diagenesis" parent="451" scope="Chemical, physical, and biological changes in sediment during and after its conversion to rock (lithification)."/><term thcode="2" code="353" name="erosion" parent="451" scope="The process whereby materials of the earth's crust are loosened, dissolved, or worn away and simultaneously moved from one place to another."/><term thcode="2" code="493" name="grain-size analysis" parent="619" scope="Method of studying soils, sediments, sands, or rock by determining the size, distribution, and proportion of selected particles."/><term thcode="2" code="500" name="gravel deposits" parent="1199" scope="Alluvial accumulations of small unconsolidated rock fragments, such as pebbles and cobbles, used in construction as fill, ground cover, or aggregate for concrete."/><term thcode="2" code="1011" name="sand deposits" parent="1199" scope="Deposits of loose particles of rock or mineral (sediment) that range in size from 0.0625-2.0 millimeters in diameter."/><term thcode="2" code="1034" name="sediment transport" parent="451" scope="Transport of solid particles of unconsolidated rock and mineral fragments, chemical precipitates, or biological materials."/><term thcode="2" code="1035" name="sedimentary rocks" parent="1005" scope="Rocks formed by the consolidation of loose, uncemented pieces of sediments."/><term thcode="2" code="1036" name="sedimentation" parent="451" scope="Process of deposition of sediments (loose, uncemented pieces of rock, mineral fragments, or biological materials).  The sediments settle out of water or air into layers on a surface."/><term thcode="2" code="1062" name="sieve-size analysis" parent="493" scope="Analytic technique determining the distribution of the different sizes of particles in soil, sediment, or rock samples by measuring the percentage that will pass through mesh holes of known size."/><term thcode="2" code="1189" name="trenching" parent="379" scope="Field method used by earth scientists to study the underground structure of an area. A long narrow ditch is dug to locate geologic features, such as a fault."/></rt></descriptor>