Features of Limestone Country

The Great Scar or Craven Limestone stretches between Wharfedale in the east to beyond Ingleborough in the west.  It is about 800 feet deep.  This massive bed of rock contains the scenic wonders of the dales: the breathtaking 260 feet high amphitheatre of Malham Cove, the awe-inspiring gorge of Gordale Scar and the brooding overhang of Kilnsey Crag.

The south west corner of the Yorkshire Dales National Park is limestone country and made from a type of limestone known as karst.  Limestone is a hard rock that is easily dissolved by the naturally slightly acidic rain and stream water.  Limestone is characterised by extensive vertical cracks or joints.  The limestone joints are so effective at removing water that streams and rivers rarely flow any distance over it.  The point where a stream disappears is called a sink. 

Sometimes this is a large obvious open hole, called a swallow hole or pot hole. One of the most famous of these is Gaping Gill on the south west slopes below Ingleborough.  In other cases the stream sinks slowly into the ground without any obvious opening, for example at Water Sinks near Malham Tarn.  When the water disappears dry stream/river beds and even dry waterfalls are left behind, for example the impressive cliffs at Malham Cove.  The stream continues underground and eventually reappears some distance away.  Occasionally after exceptionally heavy rain the streams might appear in their old bed only to disappear when the flow falls.

Over the millions of years since the limestone was laid down, water has been slowly eroding it away.  This has produced many cave and pot hole systems, some of which are extensive.  Gaping Gill’s main chamber is 110 feet high and over 6 1/2 miles of passages have been explored. The local caving clubs hold meetings at Gaping Gill and would be cavers (speleologists) and simply curious visitors can descend via a boson’s chair into the depths of Gaping Gill.  For those not feeling quite so adventurous, there are a number of smaller Show Caves that can be visited, e.g White Scar Caves at Ingleton. Stump Cross Caverns near Pately Bridge.

One of the beauties of the cave systems are the stalactites, which hang down from the ceiling and the stalagmites that grow up from the floor.  The water dripping through the small crevices in the cave roof partially evaporates and leaves behind a tiny deposit of calcium carbonate.  This gradually builds up to form a stalactite.  Stalagmites are formed from water dripping onto then floor.  Eventually the two may meet and form a vertical pillar.

Hull Pot White Scar Caves Limestone pavement Hart's Tongue Fern growing in a sheltered grike

Areas of exposed limestone are weathered and the joints in the limestone are widened by the rain water.  These eventually form a pattern of isolated blocks usually 9 to 12 inches wide and up to 12 feet deep. 

These areas are known as limestone pavement.  The vertical crevices are called grikes and the isolated blocks are called clintsThe upper surface of a clint is sometimes flat but usually they are worn into small grooves called runnels.  These are formed by water running from the top of the clint into the grike.  The grikes are ideal habitats for lime loving plants such as hart's tongue fern and herb robert.  Plants in the grikes are kept damp, sheltered and protected not only from the worst of the weather but also from the ever hungry sheep.
 
Recommended Walk
Penyghent from Horton in Ribblesdale

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