The lava seeped out arterially along the fault lines, from an ancient volcano in the hebrides (I forget the name). It then solidified forming a granite (I think) ridge. The surface rock is mostly sandstone and limestone which weathers away much more easily, leaving the bumps of the Whin Sill sticking out. Learnt that on Holy Island field trip, aged 8/9ish.


Quite apart from that, I'm frankly amazed that no-one else has commented on your desire to blow a schoolboy in a deserted forest...