APPENDIX TO THE IROQUOIS SHORE NORTH OF THE ADIRONDACKS.

In previous papers on the Iroquois shores of the Ontario basin, their position was definitely located only to a point near Belleville, on the northern side of Lake Ontario. But, from the general character of the country, I pointed out the necessity of extending the Iroquois water across a broad expanse of country to the highlands north of the Ottawa river, on the flanks of which shore deposits are known at various localities. I have a'so shown that the Iroquois water stood at or near sea-level; and in my working hypothesis considered the Iroquois water as an extension of the gulf of Saint Lawrence into the Ontario basin, although more or less obstructed by ice. Since the last paper was written, Mr. G. K. Gilbert and myself have revisited the region as far as a point 100 miles northeast of Watertown. Owing to Mr. Warren Upham's recent acceptance of the extension of the open Iroquois water as far as Quebec, it becomes desirable that the old shore line, so far as definitely surveyed, should be published.

After a long stretch of unbroken continuity, the Iroquois beach is abruptly interrupted by rocky cliffs on the side of the escarpment about five miles east of Watertown. Beyond this point, owing to the broken continuity, the remmants of the ancient shore are more or less fragmentary. The old subaqueous plain extends up the broad Black river valley far above Carthage, with gravel deposits characterizing portions of its margin. The northeastward elevation of the Iroquois beach in this region rises at over six feet per mile. Beyond Carthage, the country becomes more broken, being traversed by ridges of crystalline rocks, forming a late extension of the archipelago of the Thousand Islands at a higher level. The drift deposits become more sandy, with very little clay, and consequently are less favorable for the production of well defined beaches. The island character of this region is particularly unfavorable for the development of well defined shore markings. But wherever valleys enter the archipelago, their outlets are characterized by delta deposits of terraces, whose hypsometric position can be predicted in proceeding eastward.

At Mr. Frank Wilson's, four miles east of Watertown, the unquestioned beach is broken into ridgelets between 730 and 704 feet, with a frontal gravel-bearing terrace at 682 feet. Below this horizon there is an extensive terrace plain east of Watertown at about 535 feet. At the mouth of Indian river, at Natural Bridge, these delta deposits form terraces, with more or less beach structure, at an elevation between 829

any more than the narrow channels among the gigantic islands north of Hudson Bay would prove the former presence of a dam holding in the waters of that bay, were the whole country elevated. For a glacial dam to exist across the Adirondacks, even at the narrowest point, it would need to be 80 or 100 miles wide. If it had no greater depth than the water north of Fine used to have, the ice would need to be thick enough to fill a channel of 800 feet depth. As the differential uplift probably continues throughout the Adirondack region, we would need to be prepared to accept a dam of at least 1,300 feet in thickness, and a hundred miles across. *Apparent beaches in Vermont at 2,100 feet above the sea (Hitchcock),** and the post-Pleistocene emergence of Mt. Desert, observed in the coastal markings to its summit of 1,500 feet (Shaler),† increase the probability of our regional uplift continuing throughout the Adirondacks.

Any water proof dam in front of the Iroquois Beach would have had to endure throughout the long period of its formation. But all known glacial dams are small and evanescent. Yet the one suggested as closing up the Ontario's basin would have had to retain a greater sheet of open water than that of modern Lake Ontario, receiving not merely the waters of the then upper lakes, but also those of the melting of the hypothecated glacial dam. It is questionable what thickness of ice would hold in the waters, for the modern glacial dams of Mt. St. Elias discharge beneath 500 feet of ice for a distance of eight miles. As soon as the waters fell below the Mohawk outlet, the dis charge of the glacial lake ought to have melted and lowered the ice on the one side and carved out terraces on the other, unless the river were 50 to 100 miles wide. And there are terraces upon the northern side of the Ottawa valley, as well as upon the flanks of the Adirondacks. There seem to me to be no phenomena in the later lake history of Ontario necessitating the existence of a dam across the St. Lawrence valley. In short, the Iroquois water was a gulf. The Adirondacks and New England formed great islands. The Iroquois episode commenced almost synchronous with the birth of the Niagara Falls. And the history of Lake Ontario records interesting and great changes. which now form a simple story.

*NOTE - Subsequent investigations confirm the absence of glacial dams. **Geology of Vermont.

+Geology of Mt. Desert. Eighth Annual Report of U. S. Geol. Survey. Harold Topham in Proc. Roy. Geog. Soc., 1889, p. 424.

APPENDIX TO THE IROQUOIS SHORE NORTH OF THE ADIRONDACKS.

In previous papers on the Iroquois shores of the Ontario basin, their position was definitely located only to a point near Belleville, on the northern side of Lake Ontario. But, from the general character of the country, I pointed out the necessity of extending the Iroquois water across a broad expanse of country to the highlands north of the Ottawa river, on the flanks of which shore deposits are known at various localities. I have a'so shown that the Iroquois water stood at or near sea-level; and in my working hypothesis considered the Iroquois water as an extension of the gulf of Saint Lawrence into the Ontario basin, although more or less obstructed by ice. Since the last paper was written, Mr. G. K. Gilbert and myself have revisited the region as far as a point 100 miles northeast of Watertown. Owing to Mr. Warren Upham's recent acceptance of the extension of the open Iroquois water as far as Quebec, it becomes desirable that the old shore line, so far as definitely surveyed, should be published.

After a long stretch of unbroken continuity, the Iroquois beach is abruptly interrupted by rocky cliffs on the side of the escarpment about five miles east of Watertown. Beyond this point, owing to the broken continuity, the remmants of the ancient shore are more or less fragmentary. The old subaqueous plain extends up the broad Black river valley far above Carthage, with gravel deposits characterizing portions of its margin. The northeastward elevation of the Iroquois beach in this region rises at over six feet per mile. Beyond Carthage, the country becomes more broken, being traversed by ridges. of crystalline rocks, forming a late extension of the archipelago of the Thousand Islands at a higher level. The drift deposits become more sandy, with very little clay, and consequently are less favorable for the production of well defined beaches. The island character of this region is particularly unfavorable for the development of well defined shore markings. But wherever valleys enter the archipelago, their outlets are characterized by delta deposits of terraces, whose hypsometric position can be predicted in proceeding eastward.

At Mr. Frank Wilson's, four miles east of Watertown, the unquestioned beach is broken into ridgelets between 730 and 704 feet, with a frontal gravel-bearing terrace at 682 feet. Below this horizon there is an extensive terrace plain east of Watertown at about 535 feet. At the mouth of Indian river, at Natural Bridge, these delta deposits form terraces, with more or less beach structure, at an elevation between 829

and 802 feet, with a frontal gravel plain descending from 787 feet downward. In both cases, the waves, in carving out the lower terraces, have removed portions of the higher ridgelets. Between these limits there is no strongly marked terrace, but the lower is more confined to this regional topography than the upper; and where gravelly, the pebbles are subordinate to the sand. For quantity and size of waterworn pebbles, the gravel deposits at Natural Bridge are physically the equivalents of those of the Iroquois beach to the south westward. Above and below this level, at Natural Bridge, there are no fragments of ancient water lines liable to be mistaken for the Iroquois shore. The elevation of these deposits is that which would be expected from the measured warping recorded about Watertown. Beyond Natural Bridge there are extended gravel plains, in height conforming to the terraces at the old mouth of Indian river; but these are often more or less pitted.

These plains appear to me as due to the presence of floebergs or other masses of ice stranded upon the old shore. Even if they were shore deposits formed in glacial lakelets, their elevation is such as to show a common water level. They now face a lower descending country to the northwestward, and are deformed by the gradual warping toward the northeast. At Pitcairn, the valley is 200 feet or more in depth, forming a deep channel in the late expansion of the Laurentian archipelago. High on the sides of the valley zones of boulders, which are so often characteristic of old shore lines, are found at heights in keeping with the deformed Iroquois beach.

A little north of East Pitcairn, there is a fine display of terraces, with beach s'ructure. These are partly in front of a now unimportant valley. There are several ridgelets, the highest being 942 feet; but the most important is 930 feet above tide. These ridgelets descend to a terrace or frontal plain 60 feet below. A short distance beyond, the terraces of Oswegatchee river are seen. Just north of Fine, they close around and connect a rocky island with the eastern side, and form a sort of barrier beach. This bar has an elevation of 972 feet. All of the above recorded terraces were leveled. The following are of barometric measurement. The rise in height in these beaches corresponds to the deformation of the Iroquois beach, increasing from five to six and seven feet for miles toward the northeast, which amount ought perhaps to be slightly modified, owing to imperfect Reprinted from the BULL. GEOL. Soc. AM, Vol. III., p. 488-191, 1891.

identification in the crests of these terraces or the absence of some portions of the highest ridgelets.

The next great valley is that of the Grassy river. At Clifton Forge (Clarksboro), the old mouth of the valley is well defined by a beautiful gravel terrace at 1,055 feet (bar.), with an inferior terrace or ridge at 45 feet below. Lower than this no well marked gravel terrace occurs; but at 850 feet there is an extensive sand plain, forming a terrace confined to the valley. The terrace in the last valley is nearly due north of that at Fine, and appears to represent a warping of eight feet per mile, but probably the barometric measurement is responsible for the apparent increase in rate of elevation. Still, the northern uplift may probably exceed that to the northeast.

The chain of observation was continued by Mr. Gilbert and my self to Racket river. The elevations were not satisfactorily obtained, as the changing weather greatly affected the barometer, especially above South Colton. At South Colton there is a sandy plain at about 940 feet (bar.), apparently corresponding to the plains below Clifton Forge and Fine. Racket river presents an interesting change of channel near Stark post-office. Its old course was in a broad valley, now occupied by Coldwater creek as far as South Colton; but after the Pleistocene revolution, it cut across hard rocks and deserted its old channel. Following up the Coldwater valley, we reached a broad sandy terrace underlain by gravel. This plain forms terraces extending northward along the sides of the valley. Its elevation is 1,215 (? bar.; the weather was very threatening). Other deposits were noted at 1,350 feet, which were probably older valley terraces. Again, on the brow of the plateau facing Potsdam, there was a plain at 1,160 feet with a boulder pavement in front of it. The value of these measurements is impaired that they are only important in identifying continued elevations of the terrace plains near the late outlets of the valleys as far eastward as Racket river. In descending from the last plain there was no extensive valley terrace below the level of South Colton of magnitude corresponding to those at Watertown or at Clifton Forge. It might be noted that throughout this high region all of the pebbles are of local origin and none that could be identified as Canadian. The Paleozoic rocks were absent from the drift above South Colton and Parishville. Indeed, some of the apparent sandstones are cleavable quartzitic gneisses, and require close observation to prevent mistake.

Along the whole northern flank of the Adirondacks, there is a great poverty of glaciated surfaces. Near Natural Bridge the direction of