Silloth amusement arcade and the Castle Crag slate heap

I love the 2p machines in amusement arcades. Here is one at Silloth. It's the way that the coins manage to build improbable structures by stacking over each other. I know that there are often bits underneath to encourage the overhangs, but even so .....

It's a kind of emergent structure. It must be possible to model it using the laws of mechanics. I was interested in the assertion below that it is not an example of complexity.

The stacked coins remind me of stacked slates in a scree. Here is an example at the former quarry at Castle Crag.