When erosion occurs, broken down rocks form soils and are deposited in very fertile layers on valley floors and river deltas.
(erosion; occurs; ) (broken down rocks; form; soils; T:When erosion occurs) (broken down rocks; are deposited; in very fertile layers on valley floors and river deltas)
erosion broken down rocks broken down rocks
occurs form are deposited
soils T:When erosion occurs
in very fertile layers on valley floors and river deltas