A horizon
noun Geology.
the topsoil in a soil profile.
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Origin of A horizon
First recorded in 1935–40
Also called zone of leaching.
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Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for a horizon
A horizon
noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Science definitions for a horizon
A horizon
In ABC soil, the uppermost, darkest zone that is rich in organic matter. The upper section of the A horizon usually contains humus along with plant and animal matter in varying stages of decay. The middle section usually contains a high concentration of quartz or other minerals that remain following the leaching away of clay, iron, and aluminum. The lower section is typically transitional in nature between the A horizon and the B horizon. Also called zone of leaching
The American Heritage® Science Dictionary
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