New Hampshire Geology New Hampshire Bedrock Map

Precambrian Period page 4
(4600-540 million years ago)


Under the Sea

During the Protoerozoic Eon, the proto North American continent did not include what today is known as New England or the Canadian Maritime Provinces.  Much of the land that would one day create these states and provinces either lay at the bottom of the oceans or were attached to other continents at this time!

The Green Mountains of Vermont were created in the Grenville Orogeny.  An orogeny is what geologists call a mountain building event due to the collision of land masses.  The rocks that became the Green Mountains were sedimentary rocks.  These particular rocks were created from sea sediments, mostly shale (compacted muds) and limestone (the collection of skeletons of tiny sea creatures and carbonates that settled out of the ocean), off the coast of the early North American continent.  These sediments were uplifted under great pressure and temperature as a result of the land masses pushing against each other.  This great pressure and heat changed the physical nature of the shale into slate and the limestone  into marble.  When the physical characteristics of a rock are changed due to intense pressure and /or heat, geologists call the new creation metamorphic rock.

This is important for New Hampshire because most of the Granite State is not granite - which is an igneous rock created from the solidification of magma (molten rock). Most of the bedrock in New Hampshire is actually metamorphic rock!

 
Vermont Ocean Beachfront?

OceanThis image from the coast of New Hampshire shows the Atlantic Ocean as it is today.  After the Grenville Orogeny created the Green Mountains, by lifting up ocean sediments, this could have been what the coast of Vermont looked like!

(Click on the image for a closer look.)
Image Credit: Daniel E. Reidy