This weekend, I was upstate in the Hudson Valley visiting my parents, and we went hiking along the ridge of Schunemunk Mountain. While we were walking, I spotted the rock depicted in the image accompanying this post, a reddish pebble about a thumb length in diameter and cemented into a loose boulder of conglomerate the size of my head. You can probably see what it is about it that caught my attention: its surface was clearly marked with three dark, smooth, concentric ovals, almost perfectly … [Read more...]