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Limestone Deposits in the Thames River Valley: A Natural History

Limestone, a sedimentary rock, forms underwater from the compression of marine creature skeleton debris; some of these creatures include snails, clams, and corals. 

A rocky surface that is grey and white and shows some radiating fossil lines.

Close-up image of a piece of limestone with fossil traces, 2019

Geologists have classified limestone deposits in Beachville as part of the Detroit River formation from the Devonian Age. During the Devonian Age, approximately 350 million years ago, many of the earth’s continents were under shallow water. Skeletal fragments of sea creatures fell to the floor of these bodies of water, compressed together and eventually formed limestone.

In the last 2 million years, during the Pleistocene epoch, the bodies of water covering most of what is now Canada froze into vast ice sheets. When those glaciers retreated approximately 14,000 years ago, they left the landscape marked with ridges and valleys. They melted as they moved, and the lakes and waterways of Southwestern Ontario formed. Some of these ancient bodies of water would dry up, causing organic matter and soft mud to compress into limestone deposits. The Thames River Valley and the limestone corridor in Beachville are products of these geological processes.

A man walks beside layers of shattered rock

The river flats in Beachville, 1910