HISTORY OF THE LAKES 31 



local lakes. As the ice-front slowly receded northward beyond the divide 

 in an}^ section, numerous lakelets were produced between the dissolving 

 ice-front and the northward-facing land surface. Most of these were 

 evanescent and have left slight traces. Some of them, at the heads of 

 valleys, enlarged with the ice removal and may have existed long enough 

 to produce outlet channels and other phenomena characteristic of stand- 

 ing water, but not beach forms, which require considerable breadth, depth, 

 and permanence of the water body. (2) Larger local lakes. The greater 

 north-sloping valleys were occupied by lakes of large size. Each of the 

 present lakes collectively known as the " Finger " lakes was preceded 

 by a much larger and deeper glacial lake, the surface being held up to 

 the level of some outlet leading directly or indirectly southward. Similar 

 lakes also existed in some valleys in which no water is ponded today. 

 Some of these larger glacial lakes had a varied history and intricate re- 

 lationships with their neighbors. The most complex and romantic lake- 

 history belongs to the valley of the Genesee (see page 34). All of these 

 lakes were destroyed by draining to the level of adjacent lakes or to the 

 invading waters of the next group. (3) Pre- Laurentian lakes. The same 

 agenc}^ which interfered with the free drainage of the New York valleys 

 also blocked the flow in the great basins of the Saint Lawrence system. 

 For a time separate w^aters -were held in the southern or western ends of 

 Superior, Michigan, and Erie basins, known respectively as the Duluth, 

 Chicago, and Maumee glacial lakes.* Their ultimate overflow was into 

 the Mississippi. With further removal of the ice-front, the Duluth and 

 Maumee lakes were made tributary to or lost in lake Chicago, as this had 

 the lowest outlet. The water in the Erie basin, succeeding lake Maumee, 

 invaded the Ontario basin and our district of study as the glacial retreat 

 permitted. This water is called lake Warren, and is believed to have 

 covered all of the Erie basin, the lower part of Huron basin, and the 

 southern and western part of Ontario basin. Its level in central New 

 York is now lifted by the tilting of the land surface to about 880 feet. 

 The local lakes in New York were blended and lost in the eastward creep- 

 ing Warren waters, which retained their westward outlet via lake Chicago 

 to the Mississippi until the removal of the glacier from the high ground 

 near Syracuse permitted a lower escape to the Mohawk-Hudson valley. 

 When the eastward outlet of the Ontario basin was established at the 

 loAvest point, at Rome, New York, lake Iroquois came into existence. 

 From the plane of lake Warren down to that of lake Iroquois was about 

 500 feet, and the lowering of the waters, wdiich required probabh' many 



♦Description of the glacial lake phenomena of the Laurentian basins will be found in the writ 

 ings of F. B. Taylor, Warren Upham, G. K. Gilbert, J. W. Spencer, Frank Leverett, and others, 

 chiefly in this publication, in the American Geologist, and in the American Journal of Science. 



