| spodic horizon | A subsurface layer of soil characterised by the accumulation of aluminum oxides (with or without iron oxides) and organic matter, a diagnostic horizon for spodosols. (09 Oct 1997) |
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| sakuc horizon | <chemistry> A layer 6 inches or more thick comprised of secondary soluble salts. (17 Dec 1997) |
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| horizon | 1. The circle which bounds that part of the earth's surface visible to a spectator from a given point; the apparent junction of the earth and sky. "And when the morning sun shall raise his car Above the border of this horizon." (Shak) "All the horizon round Invested with bright rays." (Milton) 2. <astronomy> The unbroken line separating sky and water, as seen by an eye at a given elevation, no land being visible. 3. <geology> The epoch or time during which a deposit was made. "The strata all over the earth, which were formed at the same time, are said to belong to the same geological horizon." (Le Conte) 4. The chief horizontal line in a picture of any sort, which determines in the picture the height of the eye of the spectator; in an extended landscape, the representation of the natural horizon corresponds with this line. Apparent horizon. See Apparent. Artificial horizon, a level mirror, as the surface of mercury in a shallow vessel, or a plane reflector adjusted to the true level artificially; used chiefly with the sextant for observing the double altitude of a celestial body. Celestial horizon. <astronomy> See def. 2, above. Visible horizon. See definitions 1 and 2, above. Origin: F, fr. L. Horizon, fr. Gr. (sc) the bounding line, horizon, fr. To bound, fr. Boundary, limit. Source: Websters Dictionary (01 Mar 1998) |
| soil horizon | A distinct layer of soil, more or less parallel with the soil surface, having similar properties such as colour, texture and permeability, the soil profile is subdivided into the following major horizons: A-horizon, characterised by an accumulation of organic material. B-horizon, characterised by relative accumulation of clay iron, organic matter or aluminum. C-horizon, the undisturbed and unaltered parent material. (Some soils have an E-horizon, characterised by leaching of organic and other material.) (09 Oct 1997) |
| Streeter's developmental horizon | A term borrowed from geology and archeology by Streeter to define 23 developmental stages in young human embryos, from fertilization through the first 2 months; each horizon spanned 2 to 3 days and emphasized specific anatomic characteristics, to avoid discrepancies in the determination of age and body dimensions. Origin: G.L. Streeter (05 Mar 2000) |
| type horizon | <zoology> The geological stratum from which the name-bearing type of a nominal species or subspecies was collected. (09 Jan 1998) |
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