At the edge of the seaway, the streams meandered through a wide, flat coastal plain with deltas, shallow swamps and lagoons, accumulating plant material which would eventually form thin coal beds.
(the streams; meandered; L:At the edge of the seaway) (plant material; would form; thin coal beds; T:eventually)
the streams plant material
meandered would form
L:At the edge of the seaway
thin coal beds T:eventually