EVOLUTION OF IRONDEOUOIT VALLEY. 139 



gradient, until it is interrupted by the receding bluffs of Lake 

 Ontario. These bluffs also truncate the delta itself abruptly, espe- 

 cially, on the northeast, indicating that a large part of the original 

 deposit has been redistributed by the waves of the present lake. 



It should be noted that the Emmons plain is traceable farther 

 east than the map contours show, since the latter prove to be some- 

 what at fault. By Locke level the land is only 40 feet above the 

 Ontario water-surface of July, 1909, or approximately 290 feet A. 

 T., at the western corner of Durand-Eastman Park, while the map 

 contour here (under ''AND" in name of railway on Plate III) is 

 320. The second promontory east of this, (under "N" of Ogdens- 

 burg). also contoured 320, measures 55 feet above lake or only 305 

 A. T. Extensive grading of the park property has now obscured 

 some of these levels. 



The Emmons shore reappears east of the Bay. at Forest Lawn. 

 with a conspicuous plain above 300 feet eastward of that place, as 

 shown on the map. 



One of the most striking features connected with the Emmons 

 base-level is the great meander cut of the Genesee in its Iroquois 

 delta at the Rifle Range (west of our map) with a similar though 

 less remarkable cutting on the opposite bank. The full considera- 

 tion of these and of the complex of old channels in Seneca Park 

 must be reserved to another paper, but they are noteworthy here 

 as independent evidence of a pause in the lowering waters at a point 

 slightly above 300 feet present altitude. While Lake Emmons was 

 receiving the Genesee outwash at approximately the Charlotte coal- 

 trestles, a mile farther south the river was swinging laterally in its 

 own soft silts of an earlier stage and snaking itself about on a floor 

 of Medina sandstone as far upstream as that floor did not surmount 

 the base-level. — above which it was engaged in gorge making. The 

 material for the Windsor Beach delta was thus derived ready com- 

 minuted from this convenient supply and with great rapidity, which 

 explains why this delta deposit is so disproportionate to the wave 

 work of the evanescent Emmons waters. 



With the Emmons base-level we would associate also an ero- 

 sional terrace in the silts of the Irondequoit valley at the 320 contour. 

 This is represented by a lateral bench at two localities in the "dug- 



