480 PROCEEDINGS OF COLUMBUS MEETING. 



Lawrence nearly from east-southeasi to west-northwest in the vicinity of Quebec. 

 Thence its currents pushed up the valley by Montreal, and also down the valley, 

 filling the broad estuary of the river to the gulf; and on that tract, at or near 

 Quebec, doubtless the last remnant of the ice-harrier was melted away, allowing 

 the sea ingress westward to lake ( Ihamplain, to the mouth of lake < hitario, and to 

 Allumette island in the < Htawa. Previous to this, while an arm of the sea had been 

 washing the ice-border and thus increasing its speed of retreat in the gulf of Saint 

 Lawrence and westward to Quebec, the waves of lake Iroquois on the other side of 

 the narrowing ice-belt in this valley had likewise hastened its departure. Gradu- 

 ally this lake had extended beyond the basin of lake Ontario to fill at length the 

 lower part of the Ottawa basin, probably to the mouth of the Mattawan and pos- 

 sibly at first even crossing the watershed east of lake Nipissing, becoming thus 

 confluent with lake Algonquin — that is, the Georgian hay and lake Huron of that 

 time. It had spread eastward around the northern side of the Adirondacks to lake 

 Champlain and Montreal, and down the Saint Lawrence valley probably almost or 

 quite to Quebec, when the ice-dam between it and the sea disappeared. The glacial 

 lake Iroquois, until this time outflowing to the ocean by the Hudson river, then 

 ceased to exist ; lake Ontario became a separate sheet of fresh water; and the sea. 

 at a somewhat lower level than lake Iroquois had held, stretched to the Thousand 

 islands, where the Saint Lawrence river, at first only a few miles long and with 

 scarcely perceptible fall, discharged the outflow of lake Ontario into the prolonged 

 gulf of Saint Lawrence. 



Another part of this theme remains to be added, telling the history of the con- 

 tinuous Hudson and lake Champlain valley during the recession of the ice-sheet 

 up to the time of this opening of its northern portion to the ocean. The absence 

 of marine fossils in beds overlying the glacial drift on the shores of southern New 

 England, Long island and New .Jersey, and the water-courses which extend from 

 the terminal moraine on Long island southward across the adjacent modified drift- 

 plain and continue beneath the sea level of the Great South bay and other bays 

 between the shore and its bordering long beaches, prove that this coast stood higher 

 than now when the ice-sheet of the last glacial epoch extended to its farthest limit. 

 A measure of this elevation of the seaboard in the vicinity of New York during the 

 ( Ihamplain epoch is supplied, as I believe, by the shallow submarine channel of the 

 Hudson, which has been traced by the soundings of the United States Coast Sur- 

 vey from about VI miles off Sandy Hook to a distance of about 90 miles southeast - 

 ward.* This submerged channel, lying between the present mouth of the Hudson 

 and the very deep submarine fjord of this river, ranges from 10 to 15 fathoms in 

 depth, with an average width of 1 1 miles, along its extent of 80 miles, the depth 

 being measured from the top of its banks, which, with the adjacent sea -bed, are 

 covered by 15 to 40 fathoms of water, increasing southeastward with the slope of 

 this margin of the continental plateau. 



Luring the whole or a considerable part of the time of the glacial lake Iroquois 

 this area stretching 100 miles southeastward from New York was probably a land 

 surface, across which the Hudson flowed with a slight descent to the sea. But north- 

 ward from the present mouth of the Hudson the land in that epoch stood lower 

 than now; and the amount of its depression, beginning near the city of New York 



*A. Lindenkohl, Am. Jour. Sri.. :;,! series, vol. xxix, 1885, pp. 475-480, an. 1 vol. xli, 1891, pp. 189- 

 499; -I. I>. Dana, Am. Jour. Sci., 3d series, vol. xl, 1890, pp. 425-437, with map reduced from a chart 

 of the United States Coast Survey. 



