Br. J. W. Sjjencer — Subsidence verms Glacial Dams. 263 



has been lifted over 600 feet above its owu elevation at the head of 

 Lake Ontario.' By another series of deformed shore-lines,' it has been 

 found that the Iroquois Beach at the head of the lake has been lifted 

 its own height above the sea. Hence there is measured proof that 

 the northern side of the Adirondacks has been recently elevated a 

 thousand feet, or that it w^as recently a thousand feet lower than 

 now. The initial point of this ruovement was near the head of 

 Lake Michigan. Its maximum deformation occurs in the Adiron- 

 dacks, and amounts to six feet per mile. Whether this rise con- 

 tinues to the Atlantic, or is transformed into a depression, or is 

 faulted east of the mountains, remains a question to be determined. 

 Only fragments need be looked for east of the region already ex- 

 plored, for the deserted shore has been traced into a region of 

 broken mountains and wilderness. 



Three hundred feet above the Iroquois plain the Algonquin Beach 

 of the Huron basins is located.^ In it there is a similar deformation 

 to that recorded in the Iroquois shore, but the initial point of the 

 warping is beyond the head of Lake Michigan. With the deforma- 

 tion continuing to the north-east, it would appear that the Laurentian 

 Mountains north of the Great Lakes were very much depressed 

 during the Algonquin episode. The evidence of the formation of 

 the Algonquin Beach at sea-level has already been collected.* 



Whilst there is great deformation recorded in the higher beaches, 

 the survey's of these more broken geological records do not enable 

 us to trace the shore-lines down to sea-level, as in the case of the 

 Iroquois, and to nearly as perfect an extent, the Algonquin Beach. 

 Consequently, it is necessary to rely more fully upon the perfection 

 of the structure of the deserted shores, and upon their positions, 

 which would preclude their formation in confined lakes. Such 

 conditions exist in Ontario, Michigan, and Ohio, where extensive 

 surveys have been made. 



The lower of these shores, as the Eidgeway Beach, ^ like those 

 before named, were formed about bodies of water which opened 

 only to the north or east. But ascending a little higher, the 

 Maumee Beach*' occurs at altitudes which permitted its formation 

 in water having free communication with the Ohio and Mississippi 

 valleys by two depressions. Above this plain there are higher 

 gravel terraces and plains in Michigan, and elsewhere, notably 

 those between Kalamazoo and Marshall, with an elevation of a 

 little more than 900 feet above the sea. From them the country 

 falls away by steps towards the lakes ; but the sheet of water which 

 they once bounded had at least five connexions with the drainage 



1 "The Deformation of Iroquois Beach and Birth of Lake Ontario," by J. W. 

 Spencer, Amer. Journ. Sci. vol. xl. 1880, pp. 443-451. 



2 Ibid. p. 447. 



3 "Deformation of the Algonquia Beach and Birth of Lake Huron," by J. W. 

 Spencer, Amer. Journ. Sci. vol. xli. 1891, pp. 12-21. 



* Ibid. p. 21. 



^ " High Level Shores in the Region of the Great Lakes and their Deformation," 

 by J. W. Spencer, Amer. Journ. Sci. vol. xli. 1891. 

 6 Ibid. 



