EVOLUTION OF IRONDEQUOIT VALLEY. 149 



schema. The series of maps ( Plates IV' to X, sec c.vplamilio)i on 

 page i6o) which have been prepared to portray the sahent stages of 

 this evohition, as the writer conceives them, may henceforward 

 serve as the warp ui)on which our narrative may be woven. 



Dawson and Iroquois sedimentation. As the ice burden was 

 melting back from this region, the waters of the pro-glacial lakes 

 took up the work of burying the valley which the ice had left 

 incomplete. The waters of Dawson and Iroquois practically over- 

 topped the already concealed rock rim of the ancient valley, per- 

 mitting their sediments to level it up almost perfectly. Our first 

 map (A; Plate IV) reproduces the broader lines of the probable 

 geography during the active period of Lake Dawson. The stag- 

 nant ice, weighted with accumulated debris, lingers in the narrow 

 trough as a long slender tongue, beneath which courses an esker 

 stream that spreads its delta sands about the tip. The waters, agi- 

 tated perhaps by "iceberg calving" in a small way as well as by the 

 winds, hurl their waves upon exposed bits of the coast and keep 

 the inwashed silts beaten down to a wavebase plain. 



The stagnant tongue of ice naturally builds no important mar- 

 ginal moraines except the esker fan, and stuTace drainage upon it 

 is inconseqtiential. But the ice edge to the west is more favorably 

 situated for the discharge of many surface rivers from the melting 

 ice, just as formerly when the Pinnacle Hills were built. A series 

 of kames is therefore in construction, the position of which later 

 influenced the shaping of the Ridge Road. But so far as the valley 

 itself is concerned the deposits of this stage are localized in or 

 beyond the southern part of our map. Its outlet is just over the 

 line at the southeast, through the Fairport channel. " Though its 

 shorelines are now 480 feet above the sea, the level of the lake in 

 its own lifetime may not have been much over 200 feet above the 

 then ocean. 



The discharge from Lake Dawson entered a small lake in the 

 Syracuse-Rome region that was the beginning of Lake Iroquois. 

 But with the recession of the ice front from the drumlin hills of 

 northern Wayne county, the Dawson waters were no longer con- 

 strained to use the Fairport outlet. By flowing around north of 



