PROCEEDINGS OF THE ROCHESTER ACADEMY OF SCIENCE 



VOL. 5, PP. 123-160, PLATES 3-10. ' JULY, 1917. 



THE LAKE DEPOSITS AND EVOLUTION OF THE 

 LOWER IRONDEQUOIT \' ALLEY. 



Bv George H. Chadwick. 



Presented for publication and read by title before the Academy, 



lime 7, 1915. 



CONTEXTS. 



Introductor)-, ....... 



Physiographic Divisions, .... 



Glacial Lake Succession, ..... 



The Lake Deposits, ..... 



Earlier lakes, ..... 



Outer bar or "Ridge Road" of Iroquois, 



N'ewfane (Early Iroquois) beach at Rochester, 



Inner beaches of Iroquois, 



The silt plains, 



Iro-Genesee subaqvieous delta. 



Lake Emmons delta and terraces. 



Soundings in the Irondequoit bay 



Course and character of the "dugway" valley. 



Work of the Ontario waters, 

 Evolution of the Valley, 



Early history. 



Glacial occupation, 



Dawson and Iroquois sedimentation. 



Re-excavation; Lake Irondequoit, 



Return of Ontario waters, 



Man's contribution to the present stage. 

 Summary, ...... 



Explanation of Maps, .... 



12.3 

 124 

 124 

 12S 

 12.S 

 120 

 i:^0 

 1.31 

 133 

 136 

 13S 

 14(1 

 142 

 144 

 140 

 140 

 147 

 149 

 1.31 

 l.)7 

 1.58 

 1.59 

 160 



Introductory. 



The Irondequoit \'alley lies just to the east of the city of 

 Rochester, to whose people it is familiar as a recreation ground. 

 The main elements in its geological history have already been pre- 

 sented in these proceedings^ and elsewhere by Professor Fairchild. 

 The present paper is an outgrowth of studies upon the rock floor 

 of this valley presently to be published in which it became necessary 

 to show what features are superficial and not dominated by rock 

 forms beneath. This lateral investigation soon assumed such pro- 

 portions as to merit separate treatment, especially since its content 

 may ai>peal to a dift'erent company of students. Though prepared 

 in 1909, the manuscript has been laid aside awaiting the solution 



1. The Geology of Irondequoit Bay, H. L. Fairchild. Vol. 3: pp. 230-239. 



