MAP AND GENERAL DESCIilPTION 29 



tilted so that the water planes all rise to the northward, or east of north, 

 at a rate of two to three feet per mile. 



The local lakes were not of long duration and their surface level was 

 unstable, changing with the downcutting of the outlets and with the 

 greatly increased volume of the summer melting of the ice-sheet; con- 

 sequently true beaches are usually wanting. The conspicuous evidences 

 are the deltas of land streams with their terraces, embankments, bars 

 and spits, and the outlet channels. East of Seneca valley the evidences 

 are the same for the broader Warren and h3^per-Iroquois waters, true 

 beaches not having been found. The elevations of water-level in the 

 eastern part of the area are mainly based upon the embankments and 

 terraces, which, however, varied in their relation to the Avater surface. 

 Some of the ridges parallel or oblique to the streams were probably on 

 plateaus an uncertain distance above ordinary water ; those transverse 

 to stream channels and composed of well assorted or finer material were 

 subaqueous and sometimes many feet below the surface. The study of 

 these formations has not been carried to that degree of refinement 

 whereby the vertical relation of the terraces and embankments to the 

 water surface can be determined. The precise elevations given in the 

 paf)er were found by spirit-leveling, unless otherwise stated. 



Three shorelines are indicated on the map (plate 3). That of lake 

 Iroquois, with an elevation from Rochester to Rome of about 440 feet, 

 is represented as continuous, although from Sodus bay eastward it is 

 immature and indeterminate; that of lake Dana, which theoretically 

 extends westward throughout the Erie basin and eastward a little further 

 than lake Warren, but about 190 feet lower than Warren, is indicated 

 only where it has been continuously traced — -on the west side of Seneca 

 valley. The Warren shoreline has been traced with practical continuity 

 as far east as the meridian of Rochester, and good delta phenomena have 

 been found as far east as Owasco valley. The theoretical limits are in- 

 dicated as far eastward as the great spillway of the hypo- Warren waters 

 northeast of Skaneateles. It would have made the map confusing to 

 indicate the still higher shoreline of lake Newberry, which should oe 

 traced about the valleys of Cayuga, Seneca, Keuka, and Bristol at about 

 100 feet over the Warren plane, and opening southward at the Horse- 

 heads outlet with 900 feet elevation. 



General Description 



The records of these extinct waters are the very latest phenomena 

 connected with the ice invasion, and are the connecting link between 

 the glacial condition and the present hydrography. This Avriting is 



