Little rows of stone

The woods are full of inconspicuous little straight line stretches of cobbles. I assume these point to something in the sky but, not being a competent compass user, I don't try to figure out what. Here is a picture I took on Saturday in the woods north of Dudley Rd off Concord Rd in Billerica. That is a messy woods but here is a little structure - how old? I could fill this blog with pictures of little insconspicuous things like this. Here is one from Acton/Carlisle - taken by a friend:
As I look closely at this, I think it might be a "V" or rocks.