Paleontology and geology
The Precambrian: During the Precambrian, the area that would become Rhode Island was part of a volcanic arc called Avalonia and was located near the South Pole. There are no fossils known from these rocks.
The Paleozoic: There are no surface exposures of early Paleozoic (Cambrian through Devonian) rocks shown on this map, but a few metamorphosed sedimentary rocks can be found in the eastern part of the state. Some of these rocks contain trilobites, which provide evidence that a sea covered at least part of the state during much of this time. The metamorphism is the result of several episodes of mountain-building that occurred throughout the Paleozoic. During the Carboniferous and Permian, Pangea began to pull apart and the basin that would become Narragansett Bay (eastern Rhode Island) formed as part of this rifting. Sediments carried by rivers and streams poured into the basin, creating a low-lying, swampy area. Although these sediments were later metamorphosed, remnants of coal layers and fragments of fossil plants remain.
The Mesozoic: There are no Triassic or Jurassic rocks known from Rhode Island. This was a time when erosion outpaced deposition across the state. However, some Cretaceous gravels, sands, silts, and clays have been reported on Block Island, off the south coast of Rhode Island. These sediments may have been present over other parts of the state, but they have since been eroded away.
The Cenozoic: There are no Early Cenozoic (Tertiary) rocks in Rhode Island, as erosion continued to outpace deposition. During the Late Cenozoic (Pleistocene), vast ice sheets advanced over the state several times, as evidenced by glacial deposits and glacial striations (scratch marks) on the bedrock.