Geology of Rhode Island

The geology of Rhode Island is based on nearly one billion year old igneous crystalline basement rocks formed as part of the microcontinent Avalonia that collided with the supercontinent Gondwana.

The bedrock of Rhode Island first took shape with the emergence of a volcanic arc near a subduction on the margin of the supercontinent Gondwana, with the earliest rocks likely formed in the late Neoproterozoic.

During the early Cambrian period, as multi-cellular life rapidly increased on Earth, Avalonian basement rocks moved northward from Gondwana following the breakup of the supercontinent Pannotia.

Rhode Island became landlocked during the formation of Pangaea and experienced substantial folding during the Alleghanian orogeny leading to the creation of the Narragansett Basin.

Accumulation of sediments and organic matter accelerated during the Carboniferous period, ultimately forming small coal deposits throughout the basin.

During the breakup of Pangaea Rhode Island was positioned alongside a marine environment once again as extensive erosion of the Appalachian Mountains deposited sediments out on the continental shelf, beginning the creation of the Atlantic coastal plain.

[4] Rhode Island's surficial geology includes sediments, soil and groundwater near the surface and lying atop the bedrock lithology.

As a result of Pleistocene glaciation, much of the state is covered in glacial till including virtually all of the towns of Tiverton, Middletown, Newport, Portsmouth, Bristol, Jamestown, Burrilville and Foster.

The soils of Rhode Island are a part of the state's surficial geology, but are often studied separately because of their role in development planning, construction and agriculture.

Most soils are loamy sand and sandy loam, with medium or coarse textured grains of acid crystalline rock.

A narrow strip along the western shore of Narragansett Bay originated from Carboniferous rocks including slate and shale.

First recognized in 1846 by Orlando Smith, Westerly granite was extensively quarried between 1845 and 1955 and has been used in many of the statues at Gettysburg, Travelers Tower in Hartford, Brown University, Central Park and other locations.

In the agrarian history of early settlement in Rhode Island, quartzite was extracted from Glocester and Foster to sharpen scythes for harvesting.

In the early 19th century, efforts were briefly made to use cyanide to extract gold from rocks at Snake Den Quarry in Johnston, although no economically significant amounts were discovered.