(a) State three characteristics of limestone region (b) Describe the formation of limestone pillar. (c) In what two ways is limestone important to man?

(a) Three characteristics of a limestone (karst) region

• The surface is dry, with few surface streams because water sinks quickly through the permeable, well-jointed rock.
• The land shows underground drainage, with caves, caverns and disappearing streams (swallow holes/sink holes).
• Surface features such as clints and grikes (limestone pavements), dolines and dry valleys are common.
• Soils are thin and rocky, so the region is generally poor for agriculture.

(b) Formation of a limestone pillar

A limestone pillar (column) forms inside a cave by the joining of a stalactite and a stalagmite.

• Rainwater absorbs carbon dioxide from the air and soil to form a weak carbonic acid.
• This acidified water seeps through joints and cracks in the limestone and dissolves the calcium carbonate, carrying it in solution into the cave.
• When a drop of this water hangs from the cave roof, some water evaporates and a little calcium carbonate is deposited. Repeated dripping builds a downward-growing icicle-like feature called a stalactite.
• Water dripping onto the cave floor also deposits calcium carbonate, building an upward-growing feature called a stalagmite.
• Over a very long time the stalactite and stalagmite grow towards each other and eventually join to form a continuous limestone pillar (column).

(c) Two ways limestone is important to man

• It is used as a major raw material for the manufacture of cement.
• It is used in building (as building stone) and in the iron and steel industry as a flux, and can be used to make lime for agriculture.