Most of this is rock material which has been broken down by the action of heat, water and wind into particles of various sizes.
(Most of this; is; rock material which has been broken down by the action of heat, water and wind into particles of various sizes) (rock material; has been broken down; by the action of heat, water and wind into particles of various sizes)
Most of this rock material
is has been broken down
rock material which has been broken down by the action of heat, water and wind into particles of various sizes
by the action of heat, water and wind into particles of various sizes