More about cracked rocks

This is a picture of some rocks on the path up Scafell Pike between Lingmell Col and the summit. It has the same sort of regular cracks as the limestone pavement at Malham. These are the rocks that led Mrs B to first float the idea of earth movements being the cause. Although these rocks are volcanic, they are sedimentary in a way. The rocks are called tuff - the are made of settled volcanic ash. Yesterday's limestone is similar in that it is layers, but of the remains of sea creatures. I wonder if the particulate character of the rock means that it cracks easily if it has shear forces applied. This means a force on the top going left and force at the bottom going right, for example. However, tuff is far more resistant to weathering so you don't get the deep grykes. And I was thinking more about the huge mass that I'd calculated yesterday. How is that moved? The answer is by convection currents in the Earth's mantle. Hot magma is less dense and rises. The convection currents drag tectonic plates sideways and this can generate huge forces.