Emily Dickinson learned about geology as a student at Amherst Academy and later at the Mount Holyoke Female Seminary, both of which taught the subject from Edward Hitchcock's textbook, Elementary Geology. Hitchcock also lectured at the seminary, as did other professors from Amherst College.
In this poem, we can see that Emily had learned that the basalt ridges of the Connecticut River Valley where she lived were formed by volcanic activity millions of years previously.
Volcanoes be in Sicily
And South America,
I judge from my geography.
Volcanoes nearer here,
A lava step, at any time,
Am I inclined to climb,
A crater I may contemplate,
Vesuvius at home.