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Lee Wilder, Public Outreach Coordinator, New Hampshire Geological Survey, explains the different types of bedrock in New Hampshire. David Brooks/ Surveillance Officer

This is a simplified map of different types of bedrock in New Hampshire. Yes, simplified. Provided by the State Department of Environmental Services

The east side of Mount Cannon, washed by ice age glaciers, is the seat of the elderly in the mountains. Greg Keeler-Cannon Mountain

The Appalachian Trail along the Franken Ridge.

Like most New Hampshire people, I like the nickname "Granite State." So when I learned that, geologically speaking, this is a bit wrong, I was a little surprised.

"Our granite is less than half," Lee Wilder, the public outreach coordinator of the New Hampshire Geological Survey, told me recently.

Specifically, he said, less than half of the bedrock (the solid rock beneath our soil) in New Hampshire is actually granite. Most of these, including Mount Washington and the rest of the Presidents Range, are so-called schists.

Do you know another place where the bedrock is schist? Kilsatch Mountain-Although in an April column about the map of the state in the 19th century, I accidentally mentioned the "granite ledge" on that mountain.

Speaking of this, Wilder gave me a mild correction: "The bare rock wall at the top of the Kilthach Mountain in Warner, New Hampshire is a Devonian Glittleton Formation mica schist. This is a metamorphic rock. Granite is an igneous rock," he wrote.

Metamorphism, igneous rock, Devonian—I kind of remember those things in school. I reached out to Wilder to brush off some spiritual cobwebs, and to see if my love for state nicknames was misplaced.

We met outside the state office of the Concord Geological Survey. As a man who taught in public schools for 35 years and taught at Corbisoyer College expected, Wilder brought many educational aids. He has rock samples, lecture notes, flow charts showing how different types of rocks are formed, and even a color map of the bedrock geology of New Hampshire, which looks like it was drawn by a rotating art installation from my childhood.

The map includes 156 different categories, with names including "Highlandcroft pluton's hornblende granodiorite" and "Moat volcano". I have even heard of several types of bedrock, including Concord granite, which is mined on Rattlesnake Mountain even when we speak.

Wilder explained that the complexity of this map reflects our intricate geological history.

The bedrock beneath the soil in New Hampshire shows that for the past 500 million years, we have been part of four independent collisions between tectonic plates. The tectonic plates are a huge part of the outermost crust of the earth, carrying continents and forming the ocean floor. When these collisions occur, the resulting uplift, subsidence, and folds form a mixed bedrock.

As I remember, granite is an igneous rock, formed by the cooling of molten magma as it seeps from the lower layers. In contrast, sedimentary rocks such as limestone are formed by layers of material deposited on the seabed and squeezed over thousands of years.

The bedrock in New Hampshire is entirely igneous or a similar form called metamorphic rock, which is produced when heat and pressure change existing sedimentary or igneous rocks. By the way, this is why we don’t have any fossils to speak of: our bedrock has been heated, crushed, or melted to the point that no fossil bones can be seen.

What are the subcategories on the bedrock chart? In the past collisions between plates, they have different mineral compositions due to different time and temperature.

Granite is mainly quartz and feldspar, and some white muscovite. Wilder said that the smooth gray of Concord granite exists because it contains small particles of light-colored minerals. The equally famous Conway granite contains black biotite.

The most obvious granite in New Hampshire is the surface of Mount Cannon seen from Franconia Notch, where the old man in the mountain once lived.

"The reason the old man fell was because it had a pink feldspar, which weathered first," Wilder said. "Over time, it was eaten until it couldn't support it."

Schist is a kind of metamorphic rock, formed by multiple layers of different minerals extruded together over time, producing various colors and patterns. This is one of the reasons why hiking along Franconia Ridge is so enjoyable; schist is more interesting than most granites, which tend to be uniform in appearance.

The complexity of all these bedrocks became more complicated during the last ice age, which lasted from about 110,000 years ago to 11,000 years ago.

Glaciers move from north to south from what is now New Hampshire, then back north, then south again, and then back again, as they move, grow and melt, picking up and moving around and depositing gravel, stones, and boulders.

"If you pick up a stone in New Hampshire, it doesn't mean it will be a New Hampshire stone," Wilder said. "It could have been brought here."

In other words, the bedrock under your feet is probably not granite. The rock you can see and reach can be almost anything, but it is probably not granite.

Get to the point: Does this mean that we should actually be called a schist state? Wilder doesn't think so.

On the one hand, he worried that this nickname would cause endless jokes among fifth graders. In addition, he knew that there were not many schists in New Hampshire. We also have quite a lot of gneiss, which is of no avail, because it is pronounced "nice" and there are many nickname jokes.

But most importantly, even as a geologist, Wilder knows that geology is not everything.

"Economically speaking, this is a very important stone. This is what we know as the stone: throughout our history, we have been supplying granite," Wilder said.

He said that my worries were wrong. The status nickname is just fine.

(You can contact David Brooks at 369-3313 or dbrooks@cmonitor.com or Twitter @GraniteGeek.)

David Brooks is a journalist and writer for the science/technology column Granite Geek and the blog granitegeek.org, and the host of the monthly Science Cafe Concord event. After earning a bachelor's degree in mathematics, he became a journalist, working in Virginia and Tennessee, and then at the Nashua Telegraph for 28 years. He joined Monitor in 2015.

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