The surface features of northern Pennsylvania and southern New York consist in a broad way of an elevated plateau so extensively dissected that only small remnants remain here and there of what appears to have been once a fairly even surface. Although this country is readily accessible, and is familiar to many of our leading physiographers, no attempt so far has been made to unravel its physiographic history. Beyond a brief reference by Davis† and Tarr‡ of the surface of this plateau to the Cretaceous peneplain, nothing has been done in the way of establishing the dates of origin of the topographic features of the region. Doubtless this lack of attention in the past was due to the absence of adequate maps, but in a large measure these are being supplied, and now it is possible, by the aid of the topographic sheets at hand, to study . . .