Firstly, when running water of wind causes sedimentation, such as in a stream or on the open plains, the heavier pebbles, sands, bits of bone, etc. settle first, which the finer clays, sands and silts 
(when running water of wind; causes; sedimentation) (the heavier pebbles, sands, bits of bone, etc.; settle; T:first)
when running water of wind the heavier pebbles, sands, bits of bone, etc.
causes settle
sedimentation
T:first