Geologic History

Geologic History. . Wisconsin age glacial deposits of clay silt soils cover dolomite limestone bedrock in this area. Geologists tell us that this limestone bedrock was created 400 million years ago during the Silurian Geologic age: During this age the area we now know as Mercer County was part of a coral sea located e south of the equator. Fossils of coral, brachiepods, trilobites, and cephalopods are typical of those found in the local limestone quarry. The life forms on earth during this geologic age were marine. Plant life was just emerging on land during this period. This limestone bedrock, an important economic resource material, helped establish this area's construction and farming community. As the geologic ages progressed, this part of the North American continent moved north and raised in elevation. The Teays River flowed through this area of Mercer County until the first glacier covered the region. It was the last glacier, known as the Wisconsin, that contoured the land as we now know it. The lake location is situated on a glacial till plain between recessional moraines. The swamp area that was converted to the Grand Reservoir was formed by the arrangement of the Wabash recessional moraine. This low mound of land forms the north side of the lake. The land to the south slowly raises providing the drainage basin that still fills the lake. lt is believed that the Grand Reservoir was built on a swampy ground that is the remains of a short lived, post-glacial lake.