The land around these rivers must have been recognized as being rich, but the source of their richness was new soil deposited each year when the rivers flooded.
(The land around these rivers; must have been recognized; as being rich) (the source of their richness; was; new soil deposited each year) (new soil; deposited; T:each year when the rivers flooded) (the rivers; flooded; T:each year) (new soil; was the source of; their richness)
The land around these rivers the source of their richness new soil the rivers new soil
must have been recognized was deposited flooded was the source of
as being rich
new soil deposited each year
T:each year when the rivers flooded
T:each year
their richness