Rubble — All accumulation of loose angular rock frag- 

 ments, commonly overlying outcropping rock; the 

 unconsolidated equivalent of a breccia. GG 



Saddle — A low point on a ridge or crestline, generally a 

 divide (pass, col) between the heads of streams flowing 

 in opposite directions. HP 



Salt marsh — Flat, poorly drained land subject to periodic 

 or occasional overflow by salt water, containing water 

 that is brackish to strongly saline, and usually covered 

 with a thick mat of grassy halophytic plants; for ex- 

 ample, a coastal marsh periodically flooded by the sea, 

 or an inland marsh (or salina) in an arid region and 

 subject to intermittent overflow by water containing a 

 high concentration of salt. GG 



Sandstone — Sedimentary rock containing dominantly 

 sand-size clastic particles. HP 



Saprolite — Soft, clay-rich, thoroughly decomposed rock 

 formed in place by chemical weathering of igneous and 

 metamorphic rock. In soil science, the term saprolite is 

 applied to any unconsolidated residual material under- 

 lying the soil and grading to hard bedrock below. (See 

 residuum.) HP 



Scarp — An escarpment, cliff, or steep slope of some 

 extent along the margin of a plateau, mesa, terrace, or 

 bench. A scarp may be of any height. GG 



Scour (geomorphology) — The powerful and concentrated 

 clearing and digging action of flowing air, water, or 

 ice, especially the downward erosion by stream water 

 in sweeping away mud and silt on the outside curve of a 

 bend, or during the time of a flood. A place in a stream 

 bed swept (scoured) by running water, generally leav- 

 ing a gravel bottom. GG 



Scoria — Vesicular, cindery, crust on the surface of ande- 

 sitic or basaltic lava, the vesicular nature of which is 

 due to the escape of volcanic gases before solidifica- 

 tion; it is usually heavier, darker, and more crystalline 

 than pumice. A synonym for scoria is cinder.) HP 



Scree — A heap of rock waste at the base of a cliff or a 

 sheet of coarse debris mantling a slope. Scree is not a 

 synonym of talus, as scree also includes loose material 

 on slope without cliffs. HP 



Sediment — Solid clastic material, both mineral and or- 

 ganic, that is in suspension, is being transported, or has 

 been moved from its site of origin by water, wind, ice 

 or mass-wasting and has come to rest on the earth's 

 surface either above or below sea level. Sedimentary 

 deposits in a broad sense also include materials precipi- 

 tated from solution or emplaced by explosive volcan- 

 ism, as well as organic remains (for example, peat) that 

 have not been subject to appreciable transport. HP 



Sedimentary rock — A consolidated deposit of clastic 

 particles, chemical precipitates, and organic remains 

 accumulated at or near the surface of the earth under 

 "normal" low temperature and pressure conditions. 

 Sedimentary rocks include consolidated equivalents of 

 alluvium, colluvium, glacial drift, and eolian, lacus- 

 trine and marine deposits (for example, sandstone, silt- 

 stone, mudstone, clay-stone, and shale, conglomerate 

 and limestone, dolomite, and coal). (See sediment.) HP 



Semi-bolson — A wide desert basin or valley that is drained 

 by an intermittent stream flowing through canyons at 

 each end and reaching a surface outlet; its central playa 

 is absent or poorly developed. It may represent a bol- 

 son where the alluvial fill reached a level sufficient to 

 permit occasional overflow across the lowest divid. GG 



Shale — Sedimentary rock formed by induration of a clay 

 or silty clay deposit and having the tendency to split 

 into thin layers (that is, fissility). HP 



Shoal — adj. Having little depth; shallow, n. (a) A rela- 

 tively shallow place in a stream, lake, sea, or other 

 body of water; a shallows, (b) A submerged ridge, 

 bank, or bar consisting of or covered by sand or other 

 unconsolidated material, rising from the bed of a body 

 of water to near the surface so as to constitute a danger 

 to navigation; specif, an elevation, or an area of such 

 elevations, at a depth of 10 fathoms (formerly 6) or 

 less, composed of material other than rock or coral. It 

 may be exposed at low water. (See reef.) (c) A rocky 

 area on the sea floor within soundings, (d) A growth of 

 vegetation on the bottom of a deep lake, occurring at 

 any depth. GG 



Shoulder — The geomorphic component that forms the 

 uppermost inclined surface at the top of a hillslope. It 

 comprises the transition zone from backslope to sum- 

 mit of an upland. The surface is dominantly convex in 

 profile and erosional in origin. (See hillslope.) (fig. B-2) 

 HP 



siltstone— Sedimentary rock containing dominantly sand- 

 size clastic particles. 



Sinkhole — A closed depression formed either by solution 

 of the surficial bedrock (for example, limestone, gyp- 

 sum, salt) or by collapse of underlying caves. Com- 

 plexes of sinkholes in carbonate-rock terrain are the 

 main components of karst topography. (A synonym 

 for sinkhole is doline.) HP 



slope alluvium— Sediment gradually transported on 

 mountain or hill slopes primarily by alluvial processes 

 and characterized by particle sorting. In a profile se- 

 quence, sediments may be distinguished by differences 

 in size and/or specific gravity of coarse fragments and 



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