Region 1: Inland Basin 

The Inland Basin has many fossil-rich rocks, particularly in the Cambrian through Pennsylvanian. These rocks preserve shallow marine organisms characteristic of the diversification of marine life that occurred in the early and mid-Paleozoic. Some of the most common fossils include brachiopods, trilobites, bivalves, crinoids, and corals. In the vicinity of the coal layers found in Pennsylvania and Maryland, there is an excellent record of Pennsylvanian-age plants. 

Region 2: Appalachian/Piedmont

Similar to the Inland Basin, the Appalachian/Piedmont also contains a rich fossil record of Paleozoic sea life. However, in most cases, the fossils are not as well preserved because of the deformation and alteration of the Appalachian/Piedmont rocks by stress from the mountain-building events. Additionally, the Triassic and Jurassic rift basins that formed in this region during the breakup of Pangea preserve land animals such as dinosaurs, and freshwater organisms from lakes within the basins. 

Region 3: Coastal Plain 

The Coastal Plain sediments contain a rich record of Cretaceous and Tertiary continental shelf marine life. These marine organisms are an interesting contrast to the Paleozoic marine fossils of the Inland Basin and are evidence of the significant changes in sea life over the last several hundred million years. The most common fossils include mollusks (clams, snails and cephalopods), corals, barnacles, and sharks' teeth. The degree of preservation of Coastal Plain fossils varies widely, with many looking much like modern shells. 

Region 4: Exotic Terrane

The Exotic Terrane region is generally not fossil-rich because of the deformation and extent of igneous and metamorphic rocks caused by mountain-building events in the Paleozoic. There are, however, early Paleozoic fossil animals striking different from those found elsewhere in the Northeast. These fossils are quite similar to organisms found on the north coast of Africa, and are among the kinds of evidence that this area is a chunk removed from land on or near Africa.