Easy money.
just a sink Below surface (grade) sink
Gold found on the surface is called alluvial gold.
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I would call this convection currents in the mantle.
An intrusive igneous rock.
An intrusive igneous rock.
extrusive
The folds on the surface of the brain are called gyri.
Molten material below the surface of the Earth is called magma. It consists of molten rock, gases, and suspended solids. Magma can eventually erupt onto the Earth's surface as lava through volcanic activity.
A submarine is a ship that can travel underwater.
If it is below the water table, it is an aquifer. Otherwise I think it is just called an underground resevoir.