Sometimes I find niches with manitous or other stones standing inside. Stone was removed from this outcrop in northern RI, creating a "roof". A manitou was propped up in the resulting niche.
Here is a larger view. There don't seem to be any alignments.
This is the view from inside the niche, which faces south.
The foliated granite in this area splits easily, and thin slabs are often found in areas with quarrying. Previously, I have suggested that some manitous are thin quarried slabs that were stood up to prevent breakage (1/9/2013 ). However, this stone-in-niche arrangement occurs elsewhere, such as this one on a rocky slope facing east.
Here is another one, in a cliff which faces west over a swamp.
These last two stones are not thin slabs, and someone
set them inside these niches. It is easy to imagine these as shrines, since figure-in-niche imagery is common in churches. Perhaps these stones were placed as an offering or message to the spirit world.