Vermont’s Farmers Have Geology to Thank

Vermont’s Farmers Have Geology to Thank

Super-continent, Pangaea.
Illustration by Adelaide Tyrol

Question: Why has Vermont always been considered New England’s farm state?

Answer: Geology, as in rocks and soils.

Because of the limestone and other calcareous rocks underlying much of Vermont, its soils are generally sweeter than soils found in the rest of the region. The soils of New Hampshire and Maine, for example, tend to be more acidic, important for certain crops, such as blueberries, but not for most.

Vermont’s soils aren’t perfect for growing things. The topsoil is famously shallow, the land having been scraped by the ice sheet that covered the region 13,000 to 24,000 years ago. It’s also rocky, the result of deposits left by that last glacier when it receded. 

But Vermont’s soils, especially those in the Champlain Valley, along Lake Champlain, are well endowed with calcium, which comes from that limestone bedrock and other calcareous rock below. Calcium is a key nutrient that helps raise soil pH levels while helping to break down organic matter.

Farming is never easy. Market forces are now driving many of Vermont’s dairy farmers out of business. But these economic issues of supply and demand have nothing to do with soil quality. The state’s rich farmland means its agriculture income is still greater than that of any other New England state. And its geological past gets much of the credit.

So, what is our region’s geological story? How did natural forces work to give Vermont richer soils? The tale starts with plate tectonics, the widely accepted theory about the origins of our landscape.

According to this theory, the continents that today seem so stable are actually moving about on a sub-continental layer of more viscous rock. Over the course of hundreds of millions of years, they are pushed up against one another, then drawn apart, a flow and ebb that is infinitely slow but infinitely powerful. When they crunch together, the force is tremendous enough to raise mountain ranges; and when they pull apart, it creates ocean basins and great valleys.

Over the last billion years, three great continental collisions created the mountains of New England. These mountain-building episodes are known as orogenies, and they began with the Grenville Orogeny. Hundreds of millions of years later the Taconic and Acadian Orogenies followed, building and shaping the Green Mountains, the White Mountains and the Taconics. At one point, roughly 250 million years ago, a super-continent was formed, known as “Pangaea.” In Pangaea, all of the continents formed one great landmass, and what is now Africa was pushed up against North and South America.

Eventually, following their cyclical pattern, the proto-continents pulled apart, creating rift valleys that began filling with ocean water, where primitive ocean creatures that had shells and bodies rich in calcium lived and died, building up millions of years worth of deposits.

Over time, these ocean valleys drained leaving land that was to become Vermont, including the Champlain Valley and the Connecticut River Valley. These regions are now good agricultural areas thanks to the limy deposits from marine life.

The most recent series of geological events—ice ages in which massive, mile-thick glaciers covered the land—put the finishing touches on our region’s landscape. In Vermont, glaciers first scoured out the Champlain Basin, then they dammed in fresh water from the melting ice as they began receding. Finally as they retreated—and before the land mass depressed by the ice began rising—ocean water flowed in. Ocean creatures with calcium-rich skeletons lived in Vermont’s ancient glacial sea; these broke down and became incorporated into marine deposits that today have high carbonate content.

Vermont wound up with more limestone, while New Hampshire and points east got stuck with more acidic bedrock, the result of other geologic forces.

The Green and White Mountains, the most noticeable features of our landscapes, consist largely of igneous and metamorphic rocks, like granite, gneiss and schist. And, true to form, farms on the mountainsides were always marginal at best, and most did not last long.

Proof that ocean water once filled the lowlands we now know as the Champlain Valley was the “Charlotte Whale” unearthed by a gang of railroad workmen in the Town of Charlotte in 1849. While digging a railroad bed, they discovered a skeleton they at first thought belonged to a horse, but later was identified as that of a beluga whale, a creature of the sea.

Over the years Vermont’s rich land and its cool and moist climate made it ideal for growing grass and other forage crops for cows and sheep.

Geology has done its thing. Now it up to the human beings who control the region’s market systems to pay farmers enough for the crops, milk, meat and wool they produce.

Thomas Slayton, a Montpelier freelance writer, is editor emeritus of Vermont Life Magazine.

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