62 NEW YORK STATE MUSEUM 



the approximate location of the shore north of Richland; and plates 

 5, 6 and 7 depict the northern shore in New York in detail. For 

 future mapping there remains only three unpublished sheets, in 

 part; and the short stretch from Rome to Richland. 



A very brief outline of Lake Iroquois history may appropriately 

 close the description. The lake originated at the margin of the 

 waning Ontarian lobe of the latest ice sheet when the ice uncovered 

 the southeast part of the Ontario basin, the low ground at Rome 

 and Oneida lake. An early stage, when it reached westward only 

 to about Lyons, is mapped in plate 41, paper 160. As the ice lobe 

 gave way the lake extended itself westward until it was a narrow 

 belt of water, laving the south front of the glacier, the whole east 

 and west extent of the Ontario basin, as mapped in plate 42, of 

 160; and plate 17, of 164. 



As the Ontarian ice lobe diminished the lake increased, and 

 inserted a tongue of its water northeastward, between the ice 

 margin and the foothills of the Adirondacks. The greatest extent 

 and area of the lake was attained while the lake had its second 

 outlet at Covey pass, above described and mapped in plate i . 



The lake came to its extinction when the ice barrier on the north 

 slope of Covey hill weakened, and melted back to a height beneath 

 1030 feet, or the height of the Covey river. Then the waters were 

 permitted to drain down to sea level, and to become part of the 

 Hudson-Champlain estuary, shown in plate 2. 



Gilbert gulf. That the low altitude of the northern land at the 

 time of disappearance of the latest ice sheet must have allowed 

 oceanic waters to occupy the St Lawrence and Ontario valleys has 

 been recognized many years. As long ago as 1898 F. B. Taylor 

 mapped the Champlain sea as extending into the Ontario valley 

 (136, page 7S). 



Dr G. K. Gilbert was the first geologist to recognize the beaches 

 produced by this extension of sea-level waters (ii, page 59), and 

 called them the Oswego shore line, although they do not quite 

 reach to Oswego. 



In 1905 the writer briefly described the beaches in the southerly 

 stretch between Oswego and Clayton, and added sketch maps of 

 most of the distance (157, pages 712-18; figures 1-3) ; and took 

 the liberty of naming these marine-level waters after Doctor Gil- 

 bert, in admiring recognition of his leadership in the study of the 

 New York Pleistocene. 



In 1910 the writer extended the mapping of the Gilbert gulf 



