HWUMC

Formed from muds laid down on the sea bed 750 million years ago, this stuff has been gradually heated and compressed (metamorphosed for all you geeks), hardening into shales and then eventually into slate. Although the bedding planes may still be in evidence it is the alignment of the crystals along a "cleavage plane" which made the Victorians excited - yes, even the VIctorians got excited by cleavage.

The angle of the cleavage determined how easily the rock could be quarried and the slate of North Wales was just right - also of a very high quality it was a boom industry 100 years ago and the remnants of these quarries and mines can be seen (and explored) to this day. Very few are still working quarries and Welsh slate has now become an expensive building material, in fact a lot of slate is now imported from places like Spain.


oh... and I climbed on "the slate" for the first time Sunday just gone in Llanberis and it is fucking awesome!