In the northwestern corner of Vermont on Isle La Motte, the northernmost island of Lake Champlain, is a remarkable natural phenomenon: the Chazy Fossil Reef, 480 million years old.

It is regarded as a national treasure and was awarded the designation of National Natural Landmark by the Secretary of the US Department of the Interior and the Director of the National Park Service in January, 2009. *

The Chazy Reef  was formed during what geologists call the  Ordovician Period in a tropical sea, far to the east where Zimbabwe is today.

Located on Isle La Motte and on Valcour, Island in Lake Champlain, this unique geological formation provides scientists with an extraordinary opportunity to study primitive reef formation, shedding light on a fascinating period in the history of life on earth.

Originally the reef stretched a thousand miles from what is now Quebec to Tennessee but only a few remnants remain today.  Isle La Motte, is a “mecca” for scientists for here fossil layers reveal the story of the reef as it developed over time.

The Chazy Reef on Isle La Motte

Aerial view of south end of Isle La Motte

North America 480-450 million years ago

The Chazy Reef as it might have looked 450 mya

The Chazy Reef today

It is  difficult to imagine that 480-50 million years ago Vermont and New York States were a marine environment in a shallow tropical sea, far to the east and straddling the equator.  At that time earth was a strange and barren place.  There was no life on dry land except for a few primitive plants such as mosses and algae. Almost all of life was in the oceans. 

Carbon dioxide levels were 14-16 times higher than today with high sea levels covering much of the continents.  The continents themselves were mostly located south of the equator.

Along the continental shelf of what was to become North America, strange animals with hard exoskeletons had begun to build the first great reef community in the history of life on earth.

Over hundreds of millions of years, tectonic plate motion at a rate of less than an inch a year resulted in the  movement of the landmass now called North America from the equator to its present location.  Hence we now find fossil reefs in the unlikely locations of northern Vermont and New York.

*”The Chazy Fossil Reef is significant as the oldest known occurrence of a biologically diverse fossil reef, the earliest appearance of fossil coral in a reef environment, and the first documented example of the principle of ecological faunal succession (the process of change in an ecosystem over time.”) From “Evaluation of the Chazy Fossil Reef of Isle La Motte (VT) and Garden and Valcour Islands (NY) for its merit in Meeting National Significance Criteria as a National Natural Landmark”; Charlotte Merhtens, Ph.D.