The distribution of Paleozoic rocks has been known for a long time. Schuchert’s maps, revised from time to time and ending with the excellent set in his recently revised “Outlines of Historical Geology,” leave very little to be desired. Previously Ulrich, Willis, and others have given us very good maps. Most of these maps use the whole North American continent as a base. When such maps are reduced to the size of a page the scale is so small that local details in the United States are difficult to portray. Furthermore, scarcely any of these maps attempt to show the thickness of the rocks. In order to overcome these difficulties the writer has prepared seven maps showing the present distribution as well as the thickness of sediments for each of the periods of the Paleozoic era.
The information for these maps was obtained from the publications of the United . . .