(Jimmy of the Clue Crew displays a geological diagram on the monitor.)  It's the 2-word furniture term for the boundary between saturated & unsaturated zones of soil
Equality 
...... choke full; as full as an egg is of meat, as full as a vetch; saturated, crammed;
... [DOC] [TLE] AVKO Sample | Index for The Patterns of English Spelling 1-10 [PAR] has the effect of helping students discriminate between words such as hop, hops, 
.... in our language we may have two or more words pronounced the same but ... 
a useless word such as anhungry just because it's one of the three words in ...... 
venture fracture picture culture furniture creature .