Great Zakes, and their Deformation. 211 



It is due, in part, to the delay in systematic investigation, 

 that we owe our ignorance of the high-level shore-markings in 

 New York. Terraces and delta deposits occur about Seneca 

 and Keuka Lakes and elsewhere in New York. The gravel 

 plain at Horseheads at the divide, south of Seneca Lake valley 

 has an elevation of 900 feet. The valley is a mile or more 

 wide, with free drainage towards the south. Is this shore 

 deposit the equivalent of the Forest or some other beach? In 

 a lateral valley, immediately to the east of Horseheads, there 

 is a well marked terrace at an elevation of 1,200 feet. This 

 terrace plain could not have been formed unless the waters 

 filled the valley at Horseheads, which is only three or four 

 miles away, to a depth of 300 feet. 



The terraces of the Genesee River, up to 1,900 feet above 

 the sea, or 250 above the river, and the records north of the Adi- 

 rondack Mountains tell the same story of water everywhere, at 

 elevations indicating one vast sheet, extending over the lake 

 basins, and only obstructed by the great islands of Ontario and 

 Michigan, with beaches far higher than the now numerous val- 

 leys, radiating to the north, east, south and west. The margins 

 by this shrinking Warren Water were constantly contracting, as 

 shown by the beaches, but its full dimensions are not yet known. 



Until these investigations are further extended, this chapter 

 in the history of the lake regions cannot be completed. Its be- 

 ginning was at the close of the drift episode of the Pleistocene 

 period, and its dismemberment was the episode of the birth of 

 Algonquin and Iroquois Bays, which afterwards became lakes. 

 But whether this great sheet of water existed as an arm of the 

 sea, or a glacial lake, may be questioned by the opposing 

 schools. The absence of marine beaches seems to be an ob- 

 stacle on one side. A sheet of water, at least six or seven hun- 

 dred miles long and four hundred wide, with several, or many 

 outlets upon its southern side, appears still more unfavorable 

 to the supposition of an ice dam to the east, of more than 

 2,000 feet in thickness, beneath which a river as great as the 

 St. Lawrence was flowing, and continuing for the centuries 

 which carved out the terraces and beaches. Indeed, some of 

 the sea cliffs of the highlands of the Ontario peninsula, as well 

 as terraces and beaches indicate a long wave action. The argu- 

 ments set forth, against the glacial character of the Iroquois 

 and Algonquin Beaches, obtain with greater force when applied 

 to those of the Warren Water. But let these reasons rest in 

 abeyance, and let others enter the harvest field not circumscribed 

 by disputed hypothesis. 



Am. Jour. Sci. — Third Series, Vol. XLI, No. 243.— March, 1891. 

 14 



