Rock piles in the brook

At first I thought these were ceremonial but the presence of extensive damming and manipulations along all the brooks in this area (the headwaters of Fall Brook in Leominster/Sterling) convinced me that these rock piles are remnants of millworks. They were just older than some of the other more obvious structures.It is faintly possible that these piles were built afterwards. Nearby is a rock pile site that I do believe is ceremonial/non-practical. But to be fair there is no reason to think these are anything other than mill-work remnants. I didn't know what I was looking at while making this video clip: