I have written about piles that make a space, either with a rock or with another pile. The space, which I am calling a "gap" would be wide enough to walk through and often is angled to open towards water. Here is an example from Marble Hill, StowCloser:Can one compare this to a split rock? Some other examples here.
UPDATE: I should mention that often some interesting object or feature appears directly along the midline of the gap.