(i) STACK:
(a) FORMATION:
— Formed by wave erosion.
— Presence of a headland
— Wave erosion attacks headland at both sides
— Two waves formed in opposite sides of the headland
— Further erosion of caves produces an arch when waves joined up
— Roof of arch collapse
— The seaward portion of the headland remains as a pillar known as a stack
(b) APPEARANCE:
— Feature of the coast.
— Seaward part of the headland left standing
—Varies in size depending on the resistance of the rock.
— Further erosion of stack produces stump.
— Examples are the Needles, Oldman of Hoy.
(ii) BLOW HOLE:(a) FORMATION:
— Formed by wave erosion in a coastal cliff.
— Less resistant rock or line of weakness at the base of the cliff
— Cave is produced.
— Spray water in the cave enlarge a vertical joint in the roof.
—Hydraulic action of waves causes loose blocks to fall in.
— Wave Headland breaking into the cave may force water out of the hole known as blow hole.
(b) APPEARANCE:
— Coastal feature on a cliff. Joints and faults enlarged.
— A funnel is cut into the cliff.
— Some caves extend some distance inland beneath the cliff.
— Vertical pit is produced.
— Spray water thrown through the pit.
— Examples are found on the coast of Scotland.
(iii) SAND BAR
FORMATION:

Starts as an under water bar.
Formed by wave deposition in shallow sandy waters.
Break of the waves pushes sand towards the shore.
The back wash and under low current drags materials down the beach.
Deposition on the under water bar build up the bar

(b) APPEARANCE:
— Waves open narrow channels on it.
— Produces coastal features of an offshore bar a few metres above sea level.
— Lies parallel to the shore not continuous.
— At times covered by water at high tides and exposed at low tides