The rocks in any stone wall are unique. They vary in size, shape, color, texture, weathering, minerals and type. They even differ in the geology of how they were formed.  

What are some types of rocks we find in Portsmouth walls?  Robert Thorson

Puddingstone at Second Beach

in Exploring Stone Walls tells us that the geology of Portsmouth is classified as  “Narragansett Basin.”  Our rocks are younger and softer than the stones in the West Bay or over on the Tiverton side of the Sakonnet.  Puddingstone, Slate, Coal and Quartzite are common.  The majority are sedimentary rocks are rocks formed from sediment. They are deposited over time, and often show layers. Conglomerate sedimentary rocks form when rounded rock pieces are cemented together.  Puddingstone is a perfect example of a conglomerate and there is more puddingstone on Aquidneck Island than other places.  The best example I can give is the rock outcropping at Surfer’s End of Second Beach. Granite is in our walls as well.  It is an igneous rock.   It forms from the slow crystallization of magma below Earth’s surface. It has grains large enough to be visible with the unaided eye.  It is one of the most common rocks and is used for countertops in our kitchens.  

Our walls look different from the walls in the communities off the island.  The fieldstone that make up our walls are flatter than those in the communities off the island.  That makes them easier to work with when a wall is put together.  Our slate, for example, is layered and can be split into slabs.  Slab type stones make the best walls.