Mackinac Island in Mackinac County, Michigan — The American Midwest (Great Lakes)

Limestone Breccia

Photographed by Cosmos Mariner, July 30, 2017

1. Limestone Breccia Marker

Inscription. Mackinac Island's dramatic and beautiful rock formations and shoreline are its most striking geological features. These natural wonders, made of brecciated (broken and recemented) limestone, originated more than 350 million years ago when the Straits of Mackinac were underlain with a thick layer of rock salt several hundred feet below the surface.

Swirling underground waters slowly dissolved the rock salt, leaving large caverns below the surface. Eventually the cavern roofs collapsed leaving chimneys or stacks of broken rock.

Circulating water cemented the rocks of the stacks together producing formations harder than the surrounding unbroken rock. The erosive power of the ancient Great Lakes washed away the softer stone and exposed the breccia features.

(photo captions)
• Cavern forms
• Roof collapses
• Stacks recemented by circulating water
• Today

Made possible by a gift from Mackinac Associates

Topics. This historical marker is listed in this topic list: Natural Features.

Location. 45° 52.661′ N, 84° 38.713′ W. Marker is on Mackinac Island, Michigan, in Mackinac County. It is on Lake Shore Drive (State Highway 185) north of British Landing Road, on the left when traveling north. Marker

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is located in a pull-out on the west side of the highway, overlooking the Straits of Mackinac. Touch for map. Marker is in this post office area: Mackinac Island MI 49757, United States of America. Touch for directions.

Regionally, this marker is on Michigan’s Upper Peninsula

and on the Straits of Mackinac.

It is also in the American Midwest

and on the Great Lakes.

Globally, it is in North America,

the Great North Woods,

the Western Hemisphere,

the Western World,

and the Anglosphere.

Historically, it finds itself in what was once the Viceroyalty of New France

and also the Northwest Territory.

Other nearby markers. At least 8 other markers are within 2 miles of this marker, measured as the crow flies: The Mackinac Bridge (here, next to this marker); The Ice Bridge (a few steps from this marker); British Landing (within shouting distance of this marker); Contest for the Island (within shouting distance of this marker); People of the Water (approx. ¾ mile away); The Treaty of Washington, 1836 (approx. 0.9 miles away); Sugar Loaf (approx. 1.7 miles away); Post Cemetery (approx. 1.8 miles away). Touch for a list and map of all markers in Mackinac Island.

Photographed by Cosmos Mariner, July 30, 2017

2. Limestone Breccia Marker

(rightmost of three markers at this location)

Credits. This page was last revised on July 19, 2020. It was originally submitted on July 19, 2020, by Cosmos Mariner of Cape Canaveral, Florida. This page has been viewed 556 times since then and 36 times this year. Photos: 1, 2. submitted on July 19, 2020, by Cosmos Mariner of Cape Canaveral, Florida.