rocks. If Darwin were still alive, he might be pleased to know geologists currently estimate the age of the Earth to be 4.6 billion years.

Fossils and Stratigraphy

just off Mount Vernon Road in Southington lies a little ravine that poses big questions. The north wall of the Roaring Brook ravine reveals the metamorphic rock of the Western Uplands lying underneath Central Valley brownstone.* Geologists call this spot the "Great Unconformity," because of the jarring discord between the rocks. At the bottom of the wall are schists and above is brownstone. The schists stand on end, running vertically smack into horizontal beds of brownstone. Scattered throughout the brownstone are fragments from the underlying schists. Clearly, something has happened and, from the time of Silliman, geologists have been visiting this spot trying to figure out exactly what.

Some important conclusions can be drawn from standing a few minutes in the pleasant air of the ravine. First, because fragments of Uplands metamorphic rock are contained within the Central Valley brownstone, the brownstone must be younger than the metamorphic rock. Second, the younger brownstone was laid down on top of the older metamorphic rock. This arrangement of young rocks on top of old is found the world over and leads to a fundamental maxim of geology: the Law of Stratigraphic Succession. This law simply maintains that younger rocks, unless disturbed by major earth movements, always lie on top of older rocks. Generally speaking, the deeper one goes into the Earth's crust, the older the rocks. Young is up and old is down. Stratigraphic succession is as fundamental to a geologist's perception of reality as gravity is to a juggler.

The concept of stratigraphic succession can be applied even on a small scale. Within one exposure of brownstone bedrock, it is apparent that brownstone is composed of a succession of layers of sedimentary

*Note: this is only one of several streams in the state named Roaring Brook.

117