When I came out, Barley suggested a walk; it would be an hour before she could have our dinner ready. I didn’t like to leave the sheltering arms of the farmyard at first, but outside the lane was cool under spreading trees, and we walked by the ruins of what must have been a very fine house. Barley pulled himself over the fence and I followed. The stones had tumbled down, making a map of the original walls, and one remaining dilapidated tower gave the place a look of past grandeur. There was some hay in the half-open barn, as if that building was still used for storage. A great beam had fallen in among the stalls.
Please tell me what's the meaning of "The stones had tumbled down, making a map of the original walls,"
Thanks
