for mappers out there here's a simple trick I learned as a surveyor's assistant over 25 years ago. This method allows one to quickly draw (and or ink) rock walls.
One draws a bumpy or wavy line along the run of a wall and then repeats an alternating bump along the same run to produce an illustration of a rock wall that doesn't require one to draw a bunch of little ellipses.
Here's an example:
Draw the first line
Draw the second line
All done, you've got a rock wall.
One can easily create packed rubble walls with more jagged lines and blocks/bricks of masonry with squared off lines. Some of my walls in my last post were done with such a method.
I mostly use it to pretty up maps I have to look at frequently but different patterns can be used to convey meaningful information.