Exploration of Trenton and sub-Trenton rocks in the northern part of the Appalachian basin has been confined mainly to the shallower parts across central Ohio, southwestern Ontario, and western and central New York. Only a few wells have penetrated these rocks in the deeper parts of the basin. The salient features that have been revealed by the drilling are presented and discussed.

Maps showing the regional structure on the top of the Trenton limestone and the thicknesses of the Middle and the Upper Ordovician series in the northern part of the basin have been prepared. The lithologic characteristics of the Trenton and sub-Trenton formation across the northern part of the basin are described in six well-sample records. Their development underneath the area is shown by four series of stratigraphic sections based on well-sample records and drillers' logs.

Data are presented indicating that the dolomitic sandstones and sandy dolomites underlying the pre-Black River unconformity in central and northeastern Ohio and northwestern Pennsylvania, heretofore correlated with the St. Peter sandstone, do not represent a single geologic horizon but become progressively younger in a southerly direction in central Ohio.

Possibilities of the Trenton and sub-Trenton formations as potential sources of oil and gas are discussed.