Stack on Wall

I got pictures on a CD from Richard Potts, of Pepperrell, with several examples (reproduced with permission) of what he calls "Stack on Wall". Seeing his examples all together helps crystallize the idea that these things are anomalous.
A stack would be a structure above the level of the surrounding wall and where, often, there is a symmetry in the construction. Here is one I saw at the Stow Rd "turtle pile" site mentioned a few days ago. Here are some more of Richard's examples:

I have noticed cases where, as a wall passes over a little bump, there is a symmetric structure with lacey holes like this (from Westford):
I tell you one thing, the sun does shine through that hole sometimes and that brings to mind the idea of sun daggers.

Some day maybe we'll understand more about stone walls. If the rock piles are significant then there must be a great deal that is significant in some stone walls as well. But how are we supposed to parse this out? Perhaps anomalies like Richard's Stack on Wall can give a start. Is there any pattern to where they occur? Are there other types of wall anomalies?