Three balanced stones

I found three flat river stones resting along the border of the flowerbed. Carrying the widest one with both hands, I set it down on the garden bench to serve as a solid base. The second stone was slightly rounded and rocked back and forth when I placed it down. I waited, shifted it slowly until its groove locked in place, and then gently lowered the smallest black pebble right on top. I pulled my hands back a fraction of an inch, holding still to make sure it wouldn't topple. The tiny tower stayed upright, casting a stepped shadow across the wood.