With the dirt scrubbed off by rain, it turns out the Rock is showing its age, crisscrossed with wrinkles:
Those white lines are gouges, up to a quarter inch deep, left from the torturous journey inside the Wisconsonian glacier that dumped it in my yard. Glaciers might be slow, but they don't fool around. This one dug out the great lakes, then filled them with meltwater - that's some serious gouging. Probably some hard jolts and extreme pressure, too, as evidenced by a huge crack down the middle. It runs right through that "wound" in the center. What a story my Rock could tell! It was a long trip, too - the rocks that were left here when the glacier retreated were most likely carried down from the Upper Peninsula or Canada.
Hey, Canada - thanks for the great rocks!
You might have noticed Rock # 2 in the background. I've done enough digging (come on, you knew I wouldn't leave it alone!) to get an idea of its size. Rock # 1 measures 48 x 38, nose to tail (you figure it out.) Rock # 2's exposed surface measures 47 x 42. Uh-oh. Another big guy!