Proc. Roch. Acad. Science. 



Vol. .5, Pl. IX. 



Map F. Lake Ontario stage at a late phase with greatest extension of 

 Irondequoit Bay. Lifting of the Thousand Islands floods the Ontario 

 waters back on our region and inundates the lower Irondequoit valley 

 as far south as Zarges Mills, thus initiating the present Bay. Bar build- 

 ing is in progress already at its mouth. 



