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in beds overlying the glacial drift on the shores of southern New England, Long Island, and New Jersey, and the watercourses which extend from the terminal moraine on Long Island south ward 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 extended to its farthest limit. A measure of this elevation of the seaboard in the vicinity of New York during the Champlain epoch is supplied, as I believe, by the shallow submarine channel of the Hudson, which has been traced by the soundings of the U. S. Coast Survey from about 12 miles off Sandy Hook to a distance of about 90 miles southeastward. 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 11 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. During 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
But northward from the present mouth of the Hudson the land at that time stood lower than now; and the amount of its depression, beginning near the city of New York and increasing from south to north, as shown by terraces and deltas of the glacial Lake Hudson-Champlain, which were formed before this long and narrow lake became merged in the glacial Lake St. Lawrence, was nearly 180 feet at West Point, 275 feet at Catskill, and 310 feet at Albany and Schenectady. From these figures, however, we must subtract the amount of descent of the Hudson river, which in its channel outside the present harbor of New York may probably have been once 50 or 60 feet in its length of about 100 miles.
Before the time of disappearance of the ice-barrier from the St. Lawrence valley at Quebec, the descent of the Hudson river beyond New York city may have diminished, or the seaboard at New York may have sunk so as to bring the shore line nearly to its present position ; but the Hudson valley meanwhile had been uplifted, so that the outflow from the Lake St. Lawrence crossed the low divide, now about 150 feet above the sea, between Lake Champlain and the Hudson. This is known by the extension of fossiliferous marine deposits along the Lake Champlain basin nearly to its southern end, while they are wholly wanting along all the Hudson valley.
Indeed, the outflowing river from Lakes Iroquois, HudsonChamplain, and St. Lawrence, or the Hudson during the Postglacial period, channeled the lower part of this valley to a depth of about 100 feet below the present sea level, proving that the land there, as Merrill points out, stood so much higher than now at some time after the ice retreated.
According to the observations of Davis, Baldwin, and Baron de Geer, the highest shore line of the Lake Hudson-Champlain is now elevated to about 275 feet above the sea at Catskill, N. Y.; 550 feet in Chesterfield, N. Y., on the west side of Lake Champlain opposite to Burlington ; and 658 feet at St. Albans, Vt. Assuming that the mouth of the lake, near New York city, was 50 feet above the sea, the differential northward uplift of the originally level shore has been at the rate of about two feet
per mile for the 100 miles from the present mouth of the Hudson to Catskill ; 1.7 feet per mile for the next 160 miles north to Chestertield ; and about three and a half feet per mile in the next 30 miles north-northeastward to St. Albans. Perhaps a higher beach may exist in Chesterfield, which would bring these gradients nearer to uniformity. The series noted there by Baldwin comprises eight beaches referable to the successive water levels of Lake Hudson-Champlain, Lake St. Lawrence, and the sea in the Champlain basin, their heights above the sea level of to-day being 550 feet, 530, 470, 423, 386, 365, 335, and 290 feet. The mean level of Lake Champlain is 97 feet above the sea, and its maximum depth 402 feet. The lower four of these beaches belonged to the Champlain arm of the enlarged Gulf of St. Lawrence, as shown by the height of its sand deltas and associated fossiliferous clays; but the higher four represent stages of the Lakes Hudson-Champlain and St. Lawrence. These shore lines, like those of the glacial lakes farther west to Lake Agassiz, were probably formed during times of rest or slackening in the somewhat intermittent epeirogenic elevation of the land.
Lake St. Lawrence.*_ The records of the Glacial and Champlain epochs in the St. Lawrence valley have been most fully studied during many years by Sir William Dawson, to whose work chiefly we are indebted for detailed descriptions of the evidences of the marine submergence of that region to a maximum height at Montreal somewhat exceeding 500 feet above the present sea level. Earlier than that time of occupation of the depressed broad valley by the sea, it was filled from Lake Ontario to near Quebec, by a great glacial lake, held on its northeast side by the receding continental ice-sheet. The directions of the glacial striæ and transportation of the drift in the St. Lawrence valley, running southwestward at Montreal and onward to the great lakes, but eastward from Quebec down the shores of the Gulf of St. Lawrence, and southeast across Nova Scotia and New Brunswick, show that the latest remnant of the ice barrier blockading this valley was melted away in the neighborhood of Quebec, then admitting the sea to a large, low region westward. Until this barrier was removed, a glacial lake, which here for convenience of description and citation is designated as the Lake St. Lawrence, dating from the confluence of Lakes Iroquois and Hudson-Champlain and growing northward and eastward, spread over the Ottawa valley probably to the mouth of the Mattawa, and down the St. Lawrence, as fast as the ice-front was melted back.
* Sir J. William Dawson, The Canadian Ice Age (Montreal, 1893), p. 301, with maps and sections, views of scenery, and nine plates of Pleistocene fossils. This volume sums up the author's work since 1855 on the glacial drift and associated lacustrine and Champlain marine formations of the St. Lawrence valley, embody. ing the studies which had been published in many papers in the “Canadian Naturalist and Geologist " and elsewhere. He had given a similar summary in a pamphlet of 112 pages, “ Notes on the Post-pliocene of Canada." in 1872. J. W. Spencer, G. K. Gilbert, Baron de Geer, S. Prentiss Baldwin, and Warren Upham, as before cited for Lakes Warren, Algonquin, Iroquois, and Hudson-Champlain.
When Lake Iroquois ceased to outflow at Rome and, after intervening stages of outlets existing for a short time at successively lower levels north of the Adirondacks, began to occupy the Champlain basin and the St. Lawrence valley northward, changing thus to the Lake St. Lawrence, its surface fell by these stages about 250 feet to the glacial Lake HudsonChamplain, which had doubtless reached northward nearly to the St. Lawrence. After this reduction of the water body in the Ontario basin, it still had a depth of about 150 feet over the present mouth of Lake Ontario, as shown by a beach traced by Gilbert, which thence rises northeastward but declines toward the south and south west. Its plane, which is nearly parallel with the higher Iroquois beaches, sinks to the present lake level near Oswego, N. Y. Farther south westward the shore of the glacial lake at this lower stage has been since submerged by Lake Ontario. The Niagara river was then longer than now, and the lower part of its extent has become covered by the present lake. From the time of the union of Lakes Iroquois and Hudson-Champlain, a strait, at first about 150 feet deep, but later probably diminished on account of the rise of the land to a depth of about 50 feet, joined the broad expanse of water in the Ontario basin with the larger expanse in the St. Lawrence and Ottawa valleys and the basin of Lake Champlain. At the subsequent time of ingress of the sea past Que. bec the level of Lake St. Lawrence fell probably 50 feet or less to the ocean level. The place of the glacial lake so far westward as the Thousand Islands was then taken by the sea, with the marine fauna which is preserved in the Leda clays and Saxicava sands.
The Champlain Marine Submergence. That the land northward from Boston was lower than now while the ice-sheet was being melted away, is proved by the occurrence of fossil mollusks of far northern range, including Leda arctica Gray, which is now found living only in the Arctic seas, preferring localities which receive muddy streams from existing glaciers and from the Greenland ice-sheet. This species is plentiful in the stratified clays resting on the till in the St. Lawrence valley and in New Brunswick and Maine, extending southward to Portsmouth, N. H. But it is known that the land was elevated from this depression to about its present height before the sea here became warm and the southern mollusks, which exist as colonies in the Gulf of St. Lawrence, migrated thither, for these southern species are not included in the extensive lists of the fossil fauna found in the beds overlying the till.
In the St. Lawrence basin these marine deposits reach to the southern end of Lake Champlain, to Ogdensburgh and Brockville, and at least to Pembroke and Allumette island, in the Ottawa river, about 75 miles above the city of Ottawa. The isthmus of Chiegnecto, connecting Nova Scotia with New Brunswick, was submerged, and the sea extended 50 to 100 miles up the valleys of the chief rivers of Maine and New Brunswick. The uplift of this region from the Champlain sea level was 10 to 25 feet in the vicinity of Boston and northeastward to Cape Ann; about 150 feet near Portsmouth, N. H.; from 150 to about 300 feet along the coast of Maine and southern New Brunswick; about 40 feet on the northwestern shore of Nova Scotia ; thence increasing westward to 200 feet in the Bay of Chaleurs, 375 feet in the St. Lawrence valley opposite the Saguenay, and about 560 feet at Montreal; 150 to 400 or 500 feet, increasing from south to north, along the basin of Lake Champlain ; about 275 feet at Ogdensburgh, and 450 feet near the city of Ottawa. The differential elevation was practically completed, as we have seen from the boreal character of the Champlain marine molluscan fauna, shortly after the departure of the ice-sheet. With the areas of the glacial Lakes Agassiz, Warren, and Iroquois, in the interior of the continent, this coastal region gives testimony of a wave-like epeirogenic elevation of the formerly ice-laden portion of the earth's crust, proportionate with the glacial melting and closely following the retreat of the ice from its boundaries of greatest Au. JOUR. Soi.-THIRD SERIES, VOL. XLIX, No. 289.-Jan., 1895.
extent inward to the areas on which its waning remnants lingered the latest.
On the Green Mountains of Vermont, the White Mountains region, and indeed probably over a large part of New England, a tract of the departing ice-sheet remained after the access of the sea to the St. Lawrence basin left the New England ice as an isolated mass. This is known by the large tribute of stratified drift quickly brought by streams from the melting ice of the Green Mountains area and deposited as gravel and sand deltas and offshore clays of the Winooski, La Moille, and Missisquoi rivers, described by Hitchcock and Baldwin, in the east border of the Champlain arm of the sea.
On the west, too, a considerable remnant of the ice-sheet seems to have remained unmelted until this time on the Adirondacks, and to have likewise supplied the deltas and marine clays of the Au Sable, Saranac, and Chazy rivers in New York. Deflections of glacial striation down the valleys, with corresponding drift transportation and formation of local moraines across some of the mountain valleys, have been recorded by Hitchcock, Stone, and others, in Vermont and New Hampshire; but the time allowed for such glacial action, under the warm Champlain climate, was very short. The earlier melting of the ice along the St. Lawrence valley than on these mountain tracts was due on one side to the laving action of the waves of Lakes Iroquois and St. Lawrence, and on the other side to the washing of the ice-cliffs by the fast encroaching sea in the Gulf of St. Lawrence, until at last near Quebec the barrier was severed.
From the Champlain submergence our Atlantic coast was raised somewhat higher than now; and its latest movement from New Jersey to southern Greenland has been a moderate depression. The vertical amount of this postglacial elevation above the present height, and of the recent subsidence, on all the coast of New Jersey, New England, and the eastern provinces of Canada, is known to have ranged from 10 feet to a maximum of at least 80 feet at the head of the Bay of Fundy, as is attested in many places by stumps of forests, rooted where they grew, and by peat beds now submerged by the sea. As in Scandinavia, the restoration of isostatic equilibrium is at. tended by miuor oscillations, the conditions requisite for repose having been overpassed by the early reëlevation of outer portions of each of these great glaciated areas. The close of the Ice age was not long ago, geologically speaking, for equilibrium of the disturbed areas has not yet been restored.