The Devonian Period, 400 to 350 million years ago, sits in the middle of the Paleozoic Era and is known for its vertebrate explosion. Sharks, boney fish, lung fish and early amphibians all appeared during this time, as did arachnids, terrestrial insects, ferns and the first tree-like plants.
Through much of the Devonian, the Catskill Sea covered most of what is now New York State; indeed, western New York harbors one of the most extensive outcrops of Devonian rocks in North America. This exposure continues along the south shore of Lake Erie, from Buffalo to the Sandusky, Ohio, area. Cliffs of Devonian shale and limestone can be found throughout this coastal region and along the rivers and streams that flow northward into the Lake. Among the more well known Devonian sediments are the Cleveland shale of the Cuyahoga River Valley and the Columbus limestone of the Marblehead Peninsula; the latter also forms the bedrock of Ohio's Lake Erie islands.
