The coastal plain mentiioned earlier is formed of Ordovician limestones and dolostones. The Ordovician begins at 505 MYA* continues up to 438 MYA; these sediments are from the earlier portion of the Ordovician.
At one place, where the sea had stripped off the overlying soil, these snails fossils were exposed. To my eye they look just like any modern snail you might see at the beach. They are extremely abundant: the beds are extensive and the fossils, most of which were 3 to 4 inches in diameter, are fairly densely packed.
I have to wonder what undersea tragedy occurred so long ago that killed and preserved all these creatures? And at the chance that brings them to light, some 500 million years later.
* MYA = million years ago