These deposits form fertile soils because they contain humus, or partially decayed plant and animal material that is rich in nutrients.
(These deposits; form; fertile soils; because they contain humus, or partially decayed plant and animal material) (they; contain; humus, or partially decayed plant and animal material) (animal material; is; rich in nutrients)
These deposits they animal material
form contain is
fertile soils because they contain humus, or partially decayed plant and animal material
humus, or partially decayed plant and animal material
rich in nutrients