Rock Piles with Bottles

In an obscure corner of the Acton Conservation Land on Nagog Hill, there is a small site with a bottle dump in the middle of it. The question of which came first is not exactly answered, but finding a bottle incorporated into into one of the rock piles suggests the dump is older than the rock piles:This bottle has an "old-timey" look to it.

On the other hand, yesterday in Shirley I found a pile with a bottle and was wanting to argue that the bottle was superficial, because it looked more modern but the pile looked reasonably smeared out:Clearly we need something more in order to conclude chronology. I want to say that in some cases the bottle or other date-able artifact is actually built into the pile - perhaps being under some of the rocks - and that in other cases it is on the surface. The former gives a clearer indication that the pile was built after the artifact. So the example here (and others, see here) are not that useful. On the other hand this one is much clearer.

For comparison, here is a bit of porcelain; and here is a broken axe. The porcelain is "old-timey" but on top of the rock pile, which provides a lower limit on the age of the pile. In the case of the axe head, one could argue that it was the rock pile, by itself. While I'm at it, here are some piles incorporating barbed wire.

To be honest though, it is likely that sites have a history and chronology of their own with some older and some newer rock piles. Increasingly I believe some of these sites were visited and used over an extended period of time. For example on Nagog Hill, there is an older sort of platform mound at the center and adjacent to the dump, and the near horizon is dotted with fresher looking piles. There is no reason to think they are all the same age.