AGE OF THE IROQUOIS BEACH 24 1 



to the northern border of Lake Algonquin, however, a considerable por- 

 tion of this water must have been restored to the sea. Hence the cor- 

 rection to be added to the 60U-foot altitude of the Algonquin beach is 

 probably much less than 100 feet. 



This horizontal plane is a useful plane of reference from which to esti- 

 mate the amount of post-x\lgonquin uplift of more northerly districts.^^ 

 The figures 50, 100, 150, etcetera, on the isobases in plate 5 may, there- 

 fore, be conceived to indicate not simply the excess of uplift along those 

 lines over uplift south of the "hinge line,^' but the total amount by which 

 the altitudes of points on those lines have been increased since the time 

 of the Algonquin beach.^^ 



The Iroquois Water-plane 

 relative ages of the iroquois beach and the algonquin beach 



The outline of Lake Iroquois in figures 1 and 2 is based on several 

 maps, but especially those of Gilbert,^* Fairchild,^^ and Coleman. ^^ The 

 location of the ice border, however, is wholly hypothetical, and shows 

 only in a rough way the position of the Ontario ice-lobe as a barrier 

 against the northwest side of the Adirondacks. The outlet into the 

 Mohawk Valley at Eome, New York, is also shown. 



It has long been thought that Lake Iroquois for at least a part of its 

 existence was a contemporary of Lake Algonquin. The channel of the 

 ancient Algonquin Eiver, apparently connecting the two lakes, first sug- 

 gested this relation.^^ More particularly, evidence seemed to have been 

 found in a great delta built by the Algonquin Eiver near Peterboro, On- 

 tario, at about the level of the Iroquois Beach.^^ Gilbert, however, re- 

 marked that the correlation of this delta with the Iroquois beach was 

 doubtful, and Coleman has more recently stated that the delta was built 

 in a small tributary lake, which he names Lake Peterboro. ^^ We can not 



22 The earliest printed statement of this idea is probably this sentence in fine print in 

 lieverett's report on the surface geology of Alcona County, Michigan Geological Survey. 

 Annual Report for 1901, p. 53 : "The departure from horizontality here in Michigan 

 may, therefore, he taken as a measure of the amount of uplift that has occurred." 



23 Goldthwait : The attitude of the Algonquin beach and its significance. (Abstract.) 

 Science, new ser., vol. 28, 1908, pp. 382-383. 



2<G. K. Gilbert: The history of Niagara River. Sixth Annual Report of the Com- 

 missioners for the State Reservation at Niagara, 1890, pp. 61-84, map, pi. 5. 



25 H. L. Fairchild : Twentieth Annual Report of the New York State Geologist, 1902, 

 pi. 19 ; and Bulletin of the New York State Museum, no. 127, 1909, pi. 42. 



2« A. F. Coleman : Bulletin of the Geological Society of America, vol. 15, 1904, pi. 22. 



^ Spencer : Proceedings of the American Association for the Advancement of Science, 

 vol. 37, 1888, pp. 198-199. 



28 Gilbert : The Algonquin River. (Abstract.) American Geologist, vol. 18, 1896, 

 p. 231. 



2» Coleman : op. clt., pp. 357-358, 



