Limestone has a peculiar quality in that whilst pure water cannot dissolve it rain water can because it has picked up carbon dioxide from the air and soil and turns the limestone into calcium bicarbonate. That process of dissolving becomes in turn a process of placing calcium carbonate when the solution is deposited, either through evaporation or by impact.

The actual dissolving happens along joints. Limestone is riven by joints (vertical) and bedding planes (horizontal). One the surface the joints are widened into grikes and the blocks left are called clints. There is a clints and grikes landscape above Malham Cove. Malham Cove itself is a large redundant waterfall because the water now goes underground through the limestone to emerge at the bottom, whereas once it flowed over the top.

taken from: http://www.change.freeuk.com/learning/geog/caves.html