The first sign that there's something unusual about the flat black rocks strewn across the shore of Lake Erie comes when Gary Lash smashes two of them together. They break easily and fall into shards that give off the faint odor of hydrocarbons, similar to the smell of kerosene. But for Lash, a geologist and professor at nearby SUNY Fredonia, smashing the rocks is a simple trick designed to catch the attention of a visitor. The black outcroppings that protrude from the nearby bluff onto the narrow beach are what really interest him.

To Lash's expert eyes, the wide band of black shale, which runs roughly parallel to the beach, reveals hundreds of millions of years of geological history. The shale formed more than 350 million years ago when organic muck settled at the bottom of the shallow sea that covered much of what is now the eastern United States; it was once buried more than two kilometers underground but has gradually risen to the surface. Now, the exposed rock shows telltale patterns of breaks and splits. "We've demonstrated that these fractures could only have formed as a result of the generation of hydrocarbons," says Lash.