IV.—On the Relations of the Middle and Upper Silurian (Clinton, Niagara, and Helderberg) Rocks of the United States

Extract

In the general classification of the Palæozoic Rocks of North America, while we have carefully compared and attempted to correlate them with the greater divisions of the Silurian, Devonian, and Carboniferous systems of Great Britain and the continent of Europe, we have still retained the local names of formations, which to a great extent were given in the Geological Survey of New York. These names, like English local names, indicate a locality or region where the strata are well shown, and the characteristic features of the formation better developed than in other places. Several of these local formations have thus been grouped together as representing certain stages in the systems of formations as recognized above.