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Bedrock

Tina Hartell

People have asked me why Vermont feels so different from its eastern neighbor New Hampshire. The two northern New England states share a yin-yang-ness in shape: southern New Hampshire’s western bulge nestled under Vermont’s Northeast Kingdom. Similar in size and climate although unique in the voting booths and motorcycle-helmet laws, these two states FEEL different sometimes as dramatically as crossing the state line. My response to this peculiarity: soil. 

A 2002 piece by Chuck Wooster out of Northern Woodlands magazine www.northernwoodlands.org  sums it up perfectly. 

“The bedrock of both states was formed side by side under the ocean off North America and then thrust above the waves by a collision between North America, Europe, and Africa. The crucial difference between the two states’ geology, however, is that Vermont is closer to the center of North America while New Hampshire is closer to the edge. This may seem overly obvious, but it has led to three significant consequences.

The first is in the composition of the bedrock itself. The entire region was underwater when the rocks of the two states were being formed – the coast was where the Adirondacks are now. Vermont, under shallow coastal water teeming with marine life, was covered by sediments rich in lime. New Hampshire, farther out to sea, was under water too deep for the formation of lime. Nearly 50% of Vermont’s bedrock is naturally rich in limy minerals. In New Hampshire, the percentage is only 5%.

If the continental collision had been a head-on car crash, Vermont would have been the trunk of the car and New Hampshire the hood. So the second consequence of location is that a sizable percentage of New Hampshire’s rocks were smashed so much that they melted together and were recast as new, crystalline rocks: the granites of the Granite State. Just under 50% of New Hampshire is underlain by crystalline rock. In Vermont, by contrast, the figure is only about 20%. Crystalline rocks erode into gravelly soils, and gravelly soils tend to be acidic because water runs right through them and washes out the soluable, acid-resistant minerals.

Third, immediately after the Ice Age, 40% of Vermont was underwater compared with only about 15% of New Hampshire. (Both states are less than 4% underwater today.) This flooding occurred because the ice sheets covering New England were heavy enough to depress the earth’s crust – by nearly 500 feet in northwest Vermont, closer to the center of continental glaciation, by 200 feet at Lebanon/White River, but scarcely at all by the New Hampshire seacoast. The soils from flooded land are rich in fine-grained clays and silts, and these soils hold moisture better, are less acidic, and are more fertile than unflooded soils.”

That’s it. 

So how does this create such differences between the states? The sweet soil –meaning calcium rich/non acidic – plays perfect host to the mixed Northern Hardwood forest, a rare forest type. Vermont is host to these rich Northern Hardwoods: maples, beech, ash, poplar. This gives Vermont the iconic red/orange foliage, the thick-trunked, tree-lined dirt roads, and the heady maple syrup industry. The less-rich New Hampshire soils have hardwoods too but more conifers dominate the acidic soils giving New Hampshire it's lovely evergreen lakes and rocky spruce outcrops. 

I aways raised an eyebrow at my obsessed rock-hunting classmates. Me, always looking at the trees. Those geologists! Whatever were they were missing?