Sheep farming. Almost all of New England was clear cut for Merino wool.

From Wikipedia:

Merino sheep were introduced to Vermont in 1812. This ultimately resulted in a boom-bust cycle for wool, which reached a price of 57 cents/pound in 1835. By 1837, 1,000,000 sheep were in the state. The price of wool dropped to 25 cents/pound in the late 1840s. The state could not withstand more efficient competition from the other states, and sheep-raising in Vermont collapsed.[39] Many sheep farmers from Vermont migrated with their flocks to other parts of the United States.