400 PROCEEDINGS OF COLUMBUS MEETING. 



plain there was no extensive valley terrace below the level of South Cotton 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 Cotton and Parishvilie. Indeed, some of the apparent sand- 

 stones are cleavable quartzitic gneisses, and require elose observation to prevent 

 mistake. 



Along the whole northern tiank of the Adirondacks, there is a great poverty of 

 glaciated surfaces. Near Natural Bridge the direction of the striae was south 7o c 

 west ami south 55° west. < hi the hills farther south the direction was south 20° to 

 25° east, and near Harrisville south 10° west. Bowlders were of large size. One, 

 at a school-house three miles southwest of South Cotton, showed at least 6,000 cubic 

 feet above surface of the ground. 



From the recent explorations, allowing for errors in observation and measure- 

 ment, it appears that shore deposits occur at the mouths of all the valleys which 

 entered the Laurentian archipelago of the Thousand islands. Throughout a con- 

 siderable range of altitude, there is only one set of terraces or delta deposits, always 

 occurring at the mouths of old valleys, with occasional connecting gravel plains or 

 terraces of beach-like structure, composed of coarse pebbles, in magnitude com- 

 parable to the physical development of the Iroquois beach farther westward ; the 

 lower terraces being mainly sandy and confined to the valleys: and the higher, if 

 known at all. much above the possible altitude of the Iroquois plain. These ter- 

 races form sets of ridgelets ranging downward from their crests about 50 feet to the 

 gravelly deposit of their frontal terraces. This holds true alike for the exposures of 

 the Iroquois beach east of Watertown and for the recorded terraces at the mouths 

 of the valley. The next great terrace plain below these gravel shores is about 

 200 feet and mostly sandy, alike near Watertown and along Grassy river and 

 elsewhere. The differential rise of the Iroquois beach increases toward the north- 

 east. Southeast of lake < >ntario it is three feet per mile. At Watertown it is five 

 or, rather, nearly six feet, and eastward the terraces at the mouths of the valleys 

 rise from six to perhaps eight feet per mile in a constantly increasing ratio, as 

 would be expected. 



Of all this cumulative evidence, there seems but one explanation, namely, that 

 these shore accumulations at the mouths of the old valley are identical with the 

 Iroquois beach further westward and formed one water level. The warping of this 

 region is established, and cannot be discarded in order to have glacial dams at 

 various elevations, which of itself appears unnecessary and illogical. But ice ob- 

 structions between these valleys at the same level would not permanently affect 

 the water level of the whole; for glacial lakes are evanescent, and some of such, if 

 they existed, would not have been more than narrow tongues, as shown by the 

 incomplete surveys. 1 do not here accept or deny the occurrence of local glacial 

 dams; only the identity of these deposits as the equivalent of the Iroquois shore 

 seems well established for a hundred miles east of Watertown. 



Mr. Upham's recently adopted hypothesis-' of the extension of open water as far 

 as Quebec during the Iroquois history, and the consequent shrinkage of the theoret- 



* Mr. Gilbert informs me that Mr. Upham refers to beaches lower than the [roquois as defined 

 by me in naming thai shore. One is scarcely expected \>< alter a definition. However, it makes 

 iini little difference which of the Ontario beaches he extends u< Quebec, as all are far above the 

 Champlain level. 



