EVOLUTION OF IRONUEOUOIT VALLEY. 



157 



thing to do with this, nevertheless they await exphcation. A com- 

 parison is suggested with the great re-entrant that hes so nearly 

 opposite them on the east side of the Bay. While we have ascribed 

 this primarily to the junction of the two silt areas, its rounded head 

 again denotes spring erosion ; and it, also, is deeply embayed. 



Return of Ontario Z'.'atcrs. The remainder of our story is soon 

 told. The returning waters of Ontario ate their way into the front 

 of the Emmons and Iroqtiois deltas, and entering the Irondequoit 

 outlet channel filled and leveled up its outer portion as they came. 

 They interrupted its cutting prematurely while there was yet a heavy 

 gradient throttgh the present narrows of the bay, then having accom- 

 plished this long climb they flooded back over the meadow plain 



Fig. 8. Typical Cross Sections. Three transverse diagrams of the lower 

 Irondequoit valley showing (9 times vertically exaggerated) the form 

 and character of the various fillings in their mutual relations. All con- 

 cealed structures necessarily theoretical. Compare Map G and, for 

 location of sections, Figure 7. 



and the river plain south of it more rapidly than sedimentation 

 could counterbalance. By this resubmergence of the meadows the 

 present Irondequoit Bay was initiated as is outlined in map F (Plate 

 IX), and once more the formerly unfilled basin begins to receive 

 sediment. Placing beside this map that of the modern stage (map 

 G, Plate X) as untouched by man, a measure is obtained of the 

 recent alluviation and of the wave work now in progress, shown also 

 in Figure 7. 



The Irondequoit has to-day either reclaimed or held its own in 

 the "dugway" section, by means of a refilling that may have a depth 

 of from twenty-five to forty feet for the lower two miles of its 

 course (sec Figures y and 8, C). Through this same portion its 



