Bedrock Geology of Vermont

Wouldn’t it be nice to be lounging on a white sand coast, soaking up the tropical sun, looking out into a clear blue, warm sea? We’d have to travel thousands of miles or – even better – millions of years into the past. Using the bedrock we can peer into deep time to discover Vermont’s ancient story of tropical seas, igneous intrusions, and continental collisions. Here you’ll find the basics of Vermont’s bedrock story and some resources that will help deepen your knowledge

Timeline of Vermont’s Bedrock

The recipe forging Vermont’s current geologic setting is simple in principle:

  1. Put Vermont in a warm tropical sea
  2. Allow 200+ million years for sediments (sands, silts, clays, fossils) to be deposited in the sea
  3. Allow time + weight of sediments to lithify these sediments into rocks (shale, limestone, sandstone)
  4. Ram another supercontinent (in fits and starts) into the supercontinent VT is part of to bake and transform the rocks (also causes gooey filling to rising up into the cupcake)
  5. Pull apart supercontinents to get some small igneous sprinkles
  6. Allow time to slowly erode the grand Himalayan sized sculpture into a gentle rolling landscape of pleasant hills and “mountains”

Over the past couple centuries, naturalists and geologists have slowly pieced together this story using evidence left behind by the slow grind of shifting plates, burrowing trilobites, photosynthetic bacteria, and igenous intrusions.

Date Event
1.2 bya Grenville orogeny (Ancestral Adirondacks formed)
600-400 mya Iapetus Ocean (Vermont is a warm tropical sea)
570-510 mya Taconic Orogeny (Iapetus Ocean begins closing, Green Mounts begin to form)
480 mya Land plants evolve (stabilizing soils, slowing erosion)
375-325 mya Acadian Orogeny (Pangea begins to form, plutons emerge)
325-360 mya Alleghenian Orogeny (last stages of Pangea formation)
136 mya  Dike swarms in Champlain Valley
136 mya – present  Erosion continues to grind down the Green Mountains from their peak heights (>20,000′)