Guided Coast to Coast Day 6

20:39


Millions of years ago, Shap was underwater. Corals and molluscs died and formed sedimentary layers on the sea bed which formed the rock called limestone. 

After crossing the M6 you see the first signs of limestone. You are out of the volcanic area of the Lakes and into Limestone Country. This is good news as Wainwright explains:

"...as every walker knows, a limestone footing invariably means easy travelling on velvet turf."

I've a feeling AW might have over estimated the general knowledge of the average walker...

He goes on to describe the limestone pavements you walk past on the first part of the walk:

"Crinkled, fissured and often grotesquely sculptured...a delight to the eye always."

Once your eyes have been suitably delighted by the limestone pavements keep them peeled for granite boulders sat on limestone. They were brought here by an ice sheet!

Throughout the walk today are several working and disused limestone quarries and lime kilns. The best example is in Smardale. 

But Pete, "What was/is the lime used for?" I hear you cry. Well, fear not, here comes a chemistry lesson...

The answer is lots of things. It can be used as a building block (the Pyramids are built from limestone) and to make cement and mortar. It is also used to produce white pigments and filler (it's in your toothpaste!). 

Chemically, limestone is calcium carbonate. If you heat it with wood or coal in a lime kiln it decomposes to calcium oxide (also called quicklime) and carbon dioxide. 

Quicklime was used in earlier times for mortars, flooring and in agriculture. It is used in the manufacture of paper, cement and petrol. It was also used for light. When heated to 2400 degrees it emits an intense glow. This was used in theatre productions and is the origin of the term "limelight". If you add water to quicklime it will release heat as it hydrates to form calcium hydroxide. This reaction is used in self-heating-cans. 

This calcium hydroxide stuff you get when putting water on quicklime is called slaked lime and it has lots of uses too such as in treating sewage, using as a lime wash on buildings, making brake pads and as an insecticide. 

Lime is also used in glass making. Silica (basically sand) has a really high melting point but if you add sodium carbonate (ash from seaweed) the temperature is lower and it is easier to work with. The only problem is that the glass will be water soluble. This is solved by adding lime. Soda-lime glass is the most common form of glass. It makes good good glasses for putting vodka, lime and soda in. 

Wainwright wouldn't have been keen. He rarely drank. Sometimes he'd have a half pint after a long walk. Maybe the 20 miles to Kirkby Stephen would deserve a whole pint? "A walker on limestone is well favoured."

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