264 Br. J. W. Spencer — Subsidence versus Glacial Dams. 



of the Mississippi system.^ Other higher terraces about more 

 insular points are found in the same region, and farther north in 

 Michigan they are said to occur at the summit of the highest land 

 east of Grand Traverse Bay at 1682 feet above tide. 



In Ontario there are well-marked sea-cliffs carved out of the 

 Niagara escarpment, as westward of Collingwood, especially at 

 elevations of from 1200 to 1425 feet above the sea. At various 

 intervals, between the plain of the Algonquin Beach and the highest 

 land of the peninsula — 1709 feet — there are also terrace and beach 

 deposits moulded out of the drift. These remnants of shores are seen 

 to within 20 feet of the highest point of land. The shore-markings 

 of these elevated lands are rendered more certain by the perfectly 

 water- worn stones, and the extent of the beach and terrace structure. 

 The sea-cliffs are too deeply graven to represent evanescent coast- 

 lines. But all of these records are interrupted owing to the topo- 

 graphy of the country, erosion by atmospheric agencies, and the 

 recent Pleistocene deformation of the region. 



Some of the positions of the surveyed coast-lines have been 

 mapped ; for a detailed list of localities reference should be made 

 to " High Level Shores in the Eegion of the Great Lakes, and their 

 Deformation." 



Again, at Dog Lake, north of Lake Superior, Professor H. Y. 

 Hind observed terraces at 1425 feet above the sea.^ 



After allowing for all the measurable Pleistocene and recent 

 deformation of the region, these elevated shores stand out so high 

 above every natural barrier, even far away to the south as well as 

 to the north, that their occurrence demands explanation by other 

 than local causes. 



The highlands of the Ontario peninsula do not form Nilometers 

 reaching more than 1700 feet above the sea; but in Potter County, 

 Western Pennsylvania, 100 miles south of Lake Ontario, they develope 

 a watershed reaching to 2680 feet above tide, with the Genesee 

 river flowing north to Lake Ontario ; the Alleghany to the Ohio 

 river; and Pine Creek to the Susquehanna. About the highest 

 flattened knob, of only a few acres in extent, and rising to within 

 twenty feet of its summit, there is a ridge of small, well water- 

 worn gravel, nearly free from sand. Mr. Carvell Lewis speaks of 

 it as kame-like,^ but its structure and form is not different from that 

 which may be true beach. This is emphasized by the occurrence 

 of a zone of boulders forming a pavement a few feet below the 

 gravel ridge — a feature so commonly developed in front of the 

 deserted beaches of the Lake region. This gravel ridge rests upon 

 the highest point of land at the very front of the "terminal 

 moraine " of Mr. Lewis, with the land declining to the north, as 

 well as falling away to the south. These gravels form a superior 

 deposit resting upon ''till" charged with angular shingle of local 



^ Cited before. 



^ " Assiniboine and Saskatchewan Expedition," 1859, p. 120. 

 ^ "A Terminal Moraine," by H. C. Lewis, Geol. Survey Pennsylvania, 

 Eept. Z, p. 143. 



