To American geologists the geographic features of the “ Finger lakes ” region are too well known to require extended description. For the purpose of this writing it will be sufficient to briefly state the relation of the lakes to the land lying immediately to the southward. These lakes, from Conesus, on the west, to Otisco, on the east, occupy deep valleys of generally north-and-south trend, and of preglacial origin. The valleys all have free drainage northward, but southward they terminate abruptly in the high land which forms the divide between the waters of the Saint Lawrence and the Susquehanna rivers. This elevation is a plateau of Portage-Chemung strata, deeply incised by the river erosion of the long ages preceding the Glacial period. The front of the great ice-sheet lingered at the northern limit of this plateau, and lobes of the retreating . . .