a-horizon

A horizon

noun Geology.
the topsoil in a soil profile.
Also called zone of leaching.
Compare B horizon, C horizon.


Origin:
1935–40

Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2013.
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Collins
World English Dictionary
A horizon
 
n
B horizon See C horizon the top layer of a soil profile, usually dark-coloured and containing humus and from which soluble salts may have been leached

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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00:10
A-horizon is always a great word to know.
So is flibbertigibbet. Does it mean:
a chattering or flighty, light-headed person.
a children's mummer's parade, as on the Fourth of July, with prizes for the best costumes.
American Heritage
Science Dictionary
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
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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