The lowest water-plane of the glacial lake Warren was about 500 feet higher in the region of their overlapping than the plane of the next important glacial lake, Iroquois. Lake Iroquois drained eastward, and, as recently shown by Taylor, lake Warren drained westward. In the epoch between the two water stages the water plane was gradually b u t not continuously lowered by the discharge of water eastward across western New York. This discharge followed successively several different lines, which were roughly parallel with one another, but cut the lines of modern drainage at right angles. Each line was characterized by a succession of glacial lakelets occupying north-south valleys, and the lakelets were connected by rivers traversing the intervening uplands. The channels of the rivers are conspicuous topographic features, having in general the character of troughs, which in drift are from 1,000 to 2,700 feet broad and in shale from 350 to 700 feet. The coarser part of the material excavated in the formation of a channel is usually found in a delta deposit at its eastern end. At various points are cliffs over which the water plunged in cataracts. There are some channels with but a single wall, the opposite wall having been constituted by the ice-front.
One of the earliest of the channels heads a few miles south of Halfway station, 14 miles west of Syracuse, and is deeply carved in Hamilton shale; its intake has an altitude of 812 feet. An important channel of later date runs from Fort Hill, north of Le Roy, to Scottsville, and is occupied in part by Oatka creek. Another extends from East Rush to Mendon; is there interrupted by the Irondequoit valley; is resumed near Victor; discontinued near Coonsville; resumed again at Elbridge, and continued to Fairmount. Yet another extends from Fairport to Lyons. South of Syracuse are three channels, quite close together, one being traversed by the Delaware, Lackawanna and Western railroad, and thence westward to Mycenae the system is somewhat complex. Most of the drainage lines end at the Iroquois shore, but others terminate, so far as traced, at higher level, indicating that before the establishment of lake Iroquois there was in the eastern part of its basin a higher base-level, probably determined by an ice-dam in the lower Mohawk valley. Near Syracuse certain of the channels are clogged by glacial drift in such way as to demonstrate a readvance of the ice after their formation by running water.
As the positions of details of the channels were determined by the relation of the ice-front to the configuration of the northward sloping land, their mapping aids in determining the trend of the ice-margin, and this trend is shown to have been approximately east and west in the Rochester-Syracuse region.
West of Clarendon the valley between the outcrops of the Niagara and Corniferous limetones appears to have held a shallow lake just after the retreat of the ice from the Niagara escarpment, and this lake initially discharged over the escarpment at five points—Clarendon, Shelby, Gasport, Lockport, and Niagara. The controlling sill on the line of Niagara river was at the Johnson ridge. Most of these overflows were of brief duration, but that at Lockport continued for a considerable period, competing with the Niagara for establishment as the perm anent outlet of lake Erie.