New Hampshire Geology New Hampshire Bedrock Map

Devonian Period
(417-354 million years ago)

Shake ...

Hold on to your seats, because an awful lot happened in the Devonian Period [deh-VOH-nee-in] in New Hampshire.  For instance, the Littleton Formation (named for Littleton, NH where the rock was first identified) was developed in much the same way as the Fitchburg Formation was during the Silurian Period.  The slow but steady collision of the North American and African tectonic plates - and the frictional heat that goes with it - squeezed the muds , marine skeletons and chalky carbonates  first into sedimentary rocks and then into very hard, erosion resistant metamorphic rocks.  Later, this collision will result in some igneous rock formation.

When tectonic plates collide, causing the Earth's surface to compact and crumple, earthquakes happen.  Earthquakes can also happen when tectonic plates separate from each other, during volcanic eruptions, from uplifting and settling.  Since all of these things have happened at one time or another in New Hampshire's history, we know there have been earthquakes here.  In fact they are still occuring.  See the box at right for more.

... and Bake

The above mentioned sediments were transformed into schist [shist], quartzite [kort-zite] and carbonate [kar-bo-nate] rocks.  These rocks are now among the hardest and most erosion resistant in the state.   

Getting caught between colliding tectonic plates and being baked by intense heat miles under the surface would make these metamorphic rocks.  The heat came from the friction of the slowly building, but ever increasing,  pressure and/or from the interior of the Earth.  See the Rock Cycle at right for more information about the different kinds of rock out there.

The Missing Link

If parts of New Hampshire's bedrock was  formed from rocks created from sea floor sediments, where are the sedimentary rocks?  Where are the fossils of sea creatures that should be embedded in those sediments?

The first question has already been partially answered. Those sediments were, for the most part, crushed between tectonic plates and baked under the heat of that collision, the heat from Earth's interior, or both.
The other part of the answer is that there has been little or no geologic building up of the Eastern portion of North America, where we live, for about 180,000,000 years or so.  That means there has only been the wearing down forces of weathering and erosion at work.  Sedimentary rocks are pretty soft and easily broken down by wind, water and glacial weathering and erosion - just look at the Grand Canyon for an example.  

There you are then:  The sedimentary rocks that formed in New Hampshire were either broken down and carried away, or they were squeezed and baked into metamorphic rocks.  There is a third option, discussed below in the section about the Concord Granite.

As for where the fossils are, they were either weathered and eroded away with the sediments they formed in, or they were caught in the metamorphosis process and were destroyed beyond recognition.  

There are, however, a few greatly distorted fossils to be found in New Hampshire, most notably on the eastern side of Mt. Moosilauke and in a few isolated spots in the Littleton area.

The Name Game

You probably already know that New Hampshire has the nickname of 'The Granite State'.  But do you know why it is called that?

Is it because most of the rock in New Hampshire is granite?  Nope.  Most rock in New Hamshire is rock other than granite.

Is it because the pioneers built their houses with granite?  Nope again.  While many house foundations were made from the stones found on that house's property, it depended on what part of the state you were in if those rocks were granite or not.  You will find some houses made of granite, but these were built well after the pioneers settled here.  Most people found it too costly in time, effort and money to build houses from granite.  Trees were much easier, and cheaper, to work with.

New Hampshire became the Granite State mainly due to the 19th Century building boom in Boston, New York City and Washington, D.C.  Other smaller cities and towns also used granite in municipal buildings and for monuments as well.  Two of the types of granite were quarried extensively  and shipped widely, spreading the fame of New Hampshire's granite.  One is a pinkish-orangish stone known as the Conway Granite and the other is a grayish stone known as the Concord Granite.  Both granites got their names from the towns they were first quarried from.

The Concord Granite

Of the two major kinds of granite exported in the building boom of the 19th Century, only the Concord Granite was formed in the Devonian Period.  Geologists beleive that the rock that is now the Concord Granite was a bed of sediments that was melted from the intense frictional heat of the continental collision.  Today, Concord Granite is still quarried for curb stone, window sills, kitchen countertops and many other uses.

Hail To The Chief(s)

If you were to name a famous mountain in the state, chances are you'd come up with Mount Washington.  It just so happens that Mount Washington and the Presidential Range are not made of granite.  These mountains are made from the very erosion resistant schists of the Littleton Formation.  Another famous mountain in the state belongs to the Littleton formation way down in the southwest corner of the state - Mount Monadnock!

The rocks of both Mount Washington and Mount Monadnock are so hard, that the rock around them has eroded away, leaving them standing so tall.

Buried Treasure

The Devonian Period's igneous rock formations also created some of the most beautiful and valuable minerals, some of which are only found in this state.  Ruggles Mine is one place where the public can visit to mine their own mineral specimens.

Earthquakes?  In New Hampshire?

Yup, we do earthquakes here.  Since colonial times, there have been ocassional reports of quite sizeable quakes that could have been 6 or 7 on the Richter Scale that caused widespread damage.  It is believed the epicenters for these larger quakes were outside of New Hampshire. Having said that, there have been a few centered in the Tamworth, Moultonborough and Ossipee area that have toppled chimneys and moved houses off their foundations!  Fortunately most quakes centered here are usually very weak.

The Rock Cycle

Rock Cycle
No, it's not some kind of extreme off-road bicycle. The Rock Cycle refers to the constant process whereby rocks are formed in one of three ways, and how they can change into any of the other types during the course of their existence.  

(Click on the image for a closer look.)|
Image credit: Earth Science Explorer

The Granite State

In granite, the three minerals crystallize as the magma cools.The longer the magma has to cool, the bigger the crystal sizes are because they have more time to organize themselves.  Look at the two pictures below.  Which type of granite had more time to cool?

Conway Granite

Concord Granite

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

The Most Climbed Mountain In The World

New Hampshire is home to the most climbed mountain in the world - Mount Monadnock.  This honor used to fall on Mount Fuji in Japan, but a tram was recently installed on that mountain. That means not all who reach the top now, climb there.  

'Monadnock' is an Abenaki term that loosely translated means 'mountain that stands alone'. As a result, geologists around the world use the term 'monadnock' to mean any hill or mountain that rises up from low lying surrounding countryside.  

The Littleton Formation appears light blue on the NH Bedrock Geologic Map.  

Can you locate where Mount Washington and Mount Monadnock are?

(Place your mouse cursor over the map for the locations.)

(Click on the image for a closer look at the map.)|

The Mountain

That Stands Alone

monadnockA view of Mt. Monadnock from Dublin Lake, Dublin, NH.

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


The "Rock Pile"

a/k/a Mount Washington

mt washington

Mt. Washington viewed from the back porch of the Mount Washington Hotel in Bretton Woods, NH.

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




Mt. Monadnock Mt. Washington