Rock Pile "altar" - Barlow School, Amenia NY

Went to my high school reunion in Amenia NY, poked my head into the woods there, and saw an isolated rock pile within a second. But then driving around the back roads amongst the dairy farms and little patches of woods, I did not see anything more. Heavy foliage blocks the view to a very dark forest under-story and most woods there are posted "No Tresspassing". So the first place I looked was also the only place I saw anything. For reference, this used to be the Viewpoint School, then it was the Barlow School, and now it is the Kildonan School. In any case, there is a wooded and very steep slope behind the main schoolhouse where I saw a pile. Many of the photos are blurry because of the lack of light under the trees and I try to avoid using the flash. Anyway...

First glimpse:Later on I noticed that there was a little pile of quartz next to the pile, in the foreground here:
As I walked up to the pile I noticed light coming through the base, suggesting the pile was hollow. It was:I never saw rocks so glued together with age. The native bedrock around here is a loose, iron filled, phyllite. Here is another view:I never saw that before and considered if it was something non-standard and perhaps not ceremonial. But there was that quartz and, about 20 feet away at the same level on the slope was a short low stretch of stone wall.Another look at the pile (I managed to hold the camera steady):
Final thoughts were along these lines: Could this be practical? It is a steep slope, so it would be practical to put it somewhere easier to get to. Did it have a function like a beehive? (no, wrong place), like an oven? (no, wrong place), like an altar? (maybe). Is the pile isolated? (no, in fact there is that small pile of quartz and the nearby low wall). In the end, this is more ceremonial than otherwise. I consider it unlikely that any of the students would know how to make such a careful rock pile.