0 a layer of rock, soil, or similar material that is below another layer:
1 something important from which something else develops, but that is not immediately obvious:
The spade dug up three inches of black soil with a substratum of yellow mud and clay.
The rich alluvial soils provide an ideal substratum for growing rice.
There's a whole substratum of administrative positions.
Many of the ancient mythical tales have a substratum of historical fact.
There was a substratum of good feeling in her.
The novel has a solid substratum of well-conceived minor characters.
Eels were sampled in the main stream at both sites which were similar in flow rate, stream width and substratum.
