New Hampshire Geology New Hampshire Bedrock Map

Carboniferous Period(354-290 million years ago)
Mississippian Period (354-323 million years ago)
Pennsylvanian Period (323-290 million years ago)

Time To Stop And Smell The Rose Quartz

Just as an awful lot happened in the Devonian Period in New Hampshire, the reverse is true of the Mississippian [miss-iss-SIPP-ee-in] and Pennsylvanian [pen-sill-VANE-yin] Periods here.  Geologically speaking, it's as if  New Hampshire slowed down a little to stop and smell the roses, or the rose quartz that was just created during the Devonian Period.  (See box at right.)  However, this does not mean that nothing happened to the landscape of New Hampshire at this time - far from it!

You might notice that the names of these two periods look like the names of two states.  They are, and there's a good reason for this.  All of the geologic time periods are named for the area on Earth where rocks of  that time period were first identified.  You may not have recognized the other locations because they are named for towns and regions in European countries.

Two For The Price Of One

The Mississippian and Pennsylvanian periods are sometimes lumped together as the Carboniferous Period [kar-bo-nif-FER-us].  You might notice the word 'carbon' in the name.  That refers to the vast coal deposits found in these two states.  Coal is almost pure carbon.  It is the remains not of any kind of rock, but of plants that lived during this time.  You may have noticed that neither time period in the Carboniferous Period is the 'New Hampshiran Period'.  This is due to two very good reasons:

Reason #1   
Coal was not discovered here first, in part because

Reason #2
no coal was formed here in New Hampshire.

Welcome To New Hompsha Mon

During the Carboniferous period, North America was straddling the Equator, with New Hampshire located just to its south.  That means the climate was tropical -  very warm and wet.  This played a key role in fostering the development of the amphibians (the ancestors of today's frogs, toads and salamanders), some of which were huge.  As a result, another name for this time period is the Age of Amphibians.  They were not the only animal type around, but they were the dominant one.  Towards the end of this age, the first reptiles showed up.  Their 'Age' was still to come and it will involve the dinosaurs.  But that's a story for another time period.

These conditions were perfect for huge fern forests (there were no 'trees'  like the ones around today just yet) and vast coal swamps.  Coal swamps are called that today because that is where all the plants grew that turned into coal later on.  They were very lush and green, not black and dirty, as the name might suggest.  These swamps were turned to coal by being buried under sediments and then squeezed under intense pressure and heat.

Sediments must flow downhill from a source that is being weathered and eroded.  What uphill source was there, and where did the pressure and heat come from?

The Press Is On

Remember the Acadian Orogeny that started back in the Ordovician Period, more than a hundred million years ago?  Well it was still going on and getting ready for a final big push in our area.  The northern end of the Appalachian Mountains that we know today, were developed to their fullest extent by the end of this period.  They are thought to have rivalled today's Himalayas (correctly pronounced [him-AHL-yuz], not [him-uh-LAY-uz]) in height and majesty.

As the mountains were going up, there was weathering and erosion going on bringing sediments down the slopes to cover the coal swamps.  Over time, the coal swamps and sediments were caught up in the folding and buckling of the North American/African plate collision.  This squeeze play supplied the heat and pressure to convert the plants of the vast swamps into coal.

What Exactly Did Happen In New Hamphire Then?

Good question.  While no coal was formed here, the Northern Appalachians do run through our fair state.  That means that we have that mountain building event, in part, to thank for our current mountainous lanscape.

Intruder Alert

Not only that, but during this period, a blob of magma was rising through the crust, much like a blob of goo rises in a lava lamp.  (Ever wonder why they're called 'lava lamps'?)  It intrudes, or enters, already existing rock. In an intrusion, magma doesn't quite reach the surface.   In most cases, including this one, the intrusion stayed miles underground.   Hundreds of millions of years of weathering and erosion were needed in order to expose it as today's bedrock.  It is a special form of granite known as two-mica granite.  See  the map at right for more details.

Rose Quartz

Rose Quartz
This rose quartz can be found at the top of Pack Monadnock Mountain, near Peterborough.  (The sunglasses are there to give a sense of scale.)  Pack Monadnock is part of the Littleton Formation that was formed in the Devonian Period.

Quartz is usually made of metamorphosed silicates [SILL-ik-itz], otherwise known as sand.  Different elements mixed with the silicates give quartz its different colors (smoky, milky, clear and rose among others).

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

It's Coal - For Peat's Sake

Bituminous Coal
Bituminous Coal

Anthrasite Coal
Anthracite Coal

Coal is nothing more than fossilized peat moss that formed in vast swamps during the Carboniferous Period.  This peat moss was covered over by eons of sedimentation and then subjected to great heat and pressure.  The end result being bituminous coal (with petroleum (oil) as a by product given certain temperatures and pressure) or anthracite coal (created under even greater temperature and pressure and creating natural gas as a byproduct).

(Click on the image for a closer look.)|
Image credit: U.S. Congress

Where To Find Two Mica Granite

Granite usually contains only one kind of mica.  (See the"Granite Recipe" box on the Devonian Period page.) The granite that formed during the Carboniferous period contains two kinds of mica, making it quite unique. The two-mica granite can be seen on the map below as a dark pink shade with the city of Conway sitting in one splotch of it about halfway up the state on the Maine border side and in the Ossipee area a little south of Conway.  It can also be found on the Mid-Massachusetts border.

(Click on the image for a closer look.)|
Image credit:New Hampshire Geological Survey

Tropical New Hampshire

(Click on the image for a closer look.)|
Image credit: Christopher Scotese