Walls changing into rock piles - like a line becoming a dotted line

I was thinking about a place I found a few months ago in Sudbury (see here and here) where a stone wall ended in some scattered rock piles. I always thought piles that were in a line that extends a wall could easily be explained as a staging of rocks for building out the wall. But maybe not all the time.

There is a very big stretch of empty woods across the street at the Assabet Wildlife Refuge, so I went and dove in. Unfortunately it is a flat, undifferentiated, white pine barren with a few rocks and a few slightly higher places. So I am not sure where I was when I found another example of a wall ending in scattered rock piles. In this case the scatter ended in a junction with another wall:

Here are the three piles. Notice the larger stone in the foreground of the first picture.

Here is a view of the piles leading up to a junction. Note larger stone in the background to the left:

The wall is doing funny things there - here is a detail of the larger stone:

 

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I almost forgot about this but came across another interesting example, perhaps having no relationship - or perhaps some kind of family resemblance - as follows: Tower Hill in Boylston (of botanical garden fame) has a brook to the east that empties northward into French Brook through a little gully with brief cataracts and waterfalls. 

Just to the right in the above picture the wall ends with a few scattered rock piles in and next to the brook.

You almost can't make them out. But I convinced myself they were really there.