Correspondence. 63 
Wright, Baldwin, the present writer, and others, these latest explora- 
tions and discussions by Air. Taylor enable us to forma very definite 
and closely connected historical si a lenient of the relationship of the ice- 
dammed lakes which preceded the present Laurentian lakes, and of their 
dependence on the gradual departure of the ice-sheet and on the accom- 
panying gradual uplift of that region. 
Before pointing oul the bearing of Mr. Taylor's work on the history of 
the glacial retreat and the volume of the Niagara river, we must note 
thai the view held by Taylor and Spencer, that the high shore 
lines around the great Laurentian lakes are of marine formation, is in- 
consistent with the total absence of marine fossiliferous beds overlying 
the glacial drift throughout the basins of these lakes. So far as the sea 
did extend, after the further recession of the ice-sheet permitted it to 
come into the St. Lawrence and Ottawa valleys and into the basin of 
lake Champlain, such marine fossils abound; but none are found above 
the Thousand Islands, which lie in the St. Lawrence at the mouth of 
lake Ontario. We may therefore confidently accept the Niagara gorge 
as a measure of all the time since that area was uncovered from the ice- 
sheet. The shore lines described by Taylor. Spencer, and others, will 
here accordingly be interpreted as records of the glacial lake Warren 
and of earlier and later ice-bound lakes.* 
Stated as concisely as possible, the highest shore at Duluth, 1,134 feel 
above the sea, at Kimball, 1,170 feet, and at Marquette, 1,190 feet, seems 
referable to the Western Superior glacial lake outflowing by the Bois 
Lruh'-St. Croix channel. To the lower lake Warren, outflowing at Chi- 
cago, with which the Western Superior lake became merged, we maj 
refer the highest shores recorded by Taylor about the north part of 
Green bay, about 600 feet above the sea. at Cook's Mill, north of this 
bay. 750 feet, at Houghton, 1,010 feet, at Sault St,'. .Marie. 1,01 I feet, and 
at lake Nipissing, 1,140 feet. With lake Warren of this extent, the ice- 
sheet had melted oil' from all the northern United States west of lake 
Nipissing and of Buffalo, N. Y.. but yet, to hold this glacial lake on the 
east, it remained unmelted upon all the Niagara and lake Ontario or 
Iroquois area. Thus we see that all the moraines within the limits of 
the United States west of the -real angle of the drift boundary near 
Salamanca, in southwestern New York, f are somewhat older than the 
moraines east of thai angle, in New York. Pennsylvania, New Jersey, 
Lou- Island, and New England. This difference in age, however, be- 
l ween the western and eastern moraines and drift was perhaps no more 
than .")i)o io 1,000 years, as we may infer from the rate of retreatof the 
portion of the ice-front forming the northern barrier of the glacial lake 
Agassiz. 
This Unexpected View of tile order rj f going of the ice-shee! I i 1 1 < 1 -- 110- 
♦Previons discussions of tlnsr i,-l.ui;il lakes by the present writer, with citattonsof 
their literature, are in the Bulletin of the Geological Society « . t America, vol. n, 1890, 
pp. 258-265; vol.ni, 1891, pp. 484487, and 508-511. 
\{ nnsult Prof. Chamberlin'a maps of the glaciated areas <>f the United States. 
I . S. Geol. Survey, Third Ann. Kep., Plates xxviu and xxxni; Seventh Ann Bep., 
Plate mil 
