GLACIAL LAKE ALGONQUIN. 445 



to present lake level at Trenton, without any indication of stopping there, it may pass 30 feet or 

 more below that level and out to the east along the Bay of Quinte. 



The great uplift which deformed the shore lines of Lakes Algonquin and Iroquois began 

 a long time after the establishment of the Kirkfield outlet — at least long enough after to allow 

 for the building of the Peterboro delta and for the making of strong shore lines over a large 

 area of the upper lakes. Coleman ' confirmed Gilbert's earlier observation that the Iroquois 

 beach splits up into a number of strands, and he found that they diverge in altitude in a direction 

 N. 20° E. from a line passing about through Quays, 6 miles north of Port Hope. Coleman con- 

 siders that south of this line the same strands diverge southward in reverse order and that all 

 but the last were submerged and obliterated. The line through Quays was therefore a nodal 

 line, and it is very significant to find that when produced parallel with the other isobases it passes 

 into the former outlet of Lake Iroquois at Rome, N. Y. But at present the Iroquois beach at 

 Quays is 97 feet higher than the same beach at Rome, apparently showing that the post-Iroquois 

 uplifts have had a stronger northward component than the earlier uplifts, for their isobases run 

 more nearly east and west. 



GLACIAL LAKE FRONTENAC. 



When the ice sheet had retreated in the St. Lawrence Valley to the northern angle of the 

 Adirondacks it opened a new outlet somewhat lower than that at Rome, N. Y. A strip along 

 the mountain side on the slope toward Lake Champlain was scoured bare by that outlet river 

 and is now known as "The Rock." This scoured channel ends in a sort of coarse delta forma- 

 tion 3 miles west of West Chazy. This stage of the lake waters was rather brief, and since the 

 ice barrier which supported it rested on the Frontenac axis of pre-Cambrian rocks, it may be 

 called glacial Lake Frontenac. A definite shore line has not yet been identified with this lake 

 stage. 



GILBERT GULF. 



After the withdrawal of the ice barrier and the fall of Lake Frontenac the sea entered the 

 basin of Lake Ontario. The duration of the marine occupation was probably short, and the 

 connection was through a shallow strait 25 or 30 miles wide. Gilbert traced the marine beach 

 on the south side of the St. Lawrence more than 25 years ago, following it from Covey Hill, 

 Quebec, near the international boundary, southwestward to Oswego, N. Y., where it passes 

 under the present level of Lake Ontario. Fairchild 2 named the marine waters in the Lake 

 Ontario basin Gilbert Gulf. 



On the Canadian side Coleman traced the marine beach from a few miles west of Prescott, 

 where he found the last of the Pleistocene marine shells, westward into the basin of Lake 

 Ontario. 3 Near Prescott the altitude of this beach is given as 350 feet above sea level. In 

 1896 what appeared to be the same upper marine limit was observed by the writer at Welch's 

 siding, 3 miles north of Smith Falls, at 460 feet. At Brighton, 6 miles southwest of Trenton, 

 Coleman gives it as 309 feet. From Brighton to Prescott the beach rises 41 feet in about 

 120 miles, or about one-third foot to the mile. But this is nearly on the line of its isobase, 

 for from Prescott to Welch's siding it rises 110 feet in about 35 miles, or more than 3 feet to 

 the mile. The direction of most rapid rise for the plane of the marine beach is therefore 

 nearly due north in this area. At Belleville the altitude of the marine beach is given as 323 

 feet, and it is calculated that at Trenton it is close to 320 feet. Thus, if it reached present 

 lake level at Trenton, Algonquin River must have descended 74 feet or more below the marine 

 beach. 



At first glance it seems hard to believe that the waters of the Lake Ontario basin could 

 have fallen so far while Algonquin River was still flowing. But during the later part of the 

 Kirkfield stage of Lake Algonquin the retreating ice was uncovering critical ground at the 

 northern angle of the Adirondacks, and large and relatively sudden lowerings of the water level 



i Bull. Geol. Soc. America, vol. 15, 1903, pp. 359, 363. 



-- Fairchild, H. L., Gilbert Gulf (marine waters in Ontario basin): Bull. Geol. Soc. America, vol. 17, 1907, p. 112. 



3 Marine and fresh-water beaches of Ontario: Bull. Geol. Soc. America, vol. 12, 1901, map, p. 130. 



