444 PLEISTOCENE OF INDIANA AND MICHIGAN. 



certainly the correlative of the Port Huron-Chicago stage of Lake Algonquin, and perhaps 

 also of Early Lake Algonquin when the volume of discharge at Buffalo was large and Lake 



Erie stood at high stage. 



TRANSITION TO LAKE IROQUOIS. 



After the separation of Lakes Erie and Ontario into two independent lakes conditions 

 changed rapidly. The ice front rested against the hills south of Syracuse, N. Y., and the out- 

 let was eastward along its front. Several of the old cataract sites and outlet channels on the 

 hills south of Syracuse are related to this shifting outlet river, though in all probability some 

 of them are older than the Wisconsin glaciation. In fact, it has been shown by Fairchild x 

 that the whole front of the escarpment from the Mohawk Valley to Ohio is marked with similar 

 channels of drainage along the border of the ice. The slope' is relatively steep, so that every 

 movement of the ice front forward or back was exceptionally effective in raising or lowering 

 the level of the lake waters to the west. This unstable condition was probably most marked 

 while the waters were finally settling down to the Iroquois level during and after separation 

 from Lake Erie. The transition stages and the lower stages confined to the Lake Ontario 

 basin must have undergone many changes of level, and these probably account in part for the 

 alternations of glacial and lacustrine formations which Spencer 2 describes as occurring in the 

 Whirlpool-St. David gorge at Niagara. 



GLACIAL LAKE IROQUOIS. 



After the separation of Lake Erie the waters in the Lake Ontario basin became independ- 

 ent, except as they received the overflow of the upper lakes through rivers or were for a brief 

 time merged in open connection with the sea. In the present state of knowledge the establish- 

 ment of synchronous events in the history of these waters and those of the upper lakes is no 

 easy task, for while much is now known concerning Lake Iroquois and Gilbert Gulf, much also 

 remains to be learned. The critical areas of Lake Iroquois showing the correlation of its 

 beaches with positions of the retreating front of the Lake Ontario ice lobe have not yet been 

 studied. Since the time of the earlier studies by Spencer, Gilbert, and the writer, Coleman's 

 investigations of the Iroquois and marine beaches have brought out many important facts 

 showing the effects of the great uplift in deforming and warping all of the beaches and in split- 

 ting the Iroquois into a number of vertically diverging strands in the northeastern part of the 

 basin. But the data on some of the critical points are still too few to yield satisfactory numeri- 

 cal values for altitude and time relations. 



Most important in its relations to these water bodies is the ancient Algonquin outlet channel. 

 Near Kirkfield and at Fenelon Falls this channel is a mile wide, and its scoured floor and faint 

 shore markings show that the water in it was 20 to 35 feet deep. It is well developed and 

 shows no sign of delta formation from its head at Kirkfield to Peterboro, where the extensive 

 gravelly plain seems to mark its delta in Lake Iroquois. Coleman 3 shows that the delta is in a 

 restricted tributary valley and in all probability marks a level slightly above that of Lake 

 Iroquois, but no serious doubt has been cast upon its general correlative relation to that lake. 

 This delta and the absence of other deltas above it show that Lake Iroquois was already in 

 existence when Algonquin River began to flow, and the strength and magnitude of the delta 

 show that the land in the region of Lake Iroquois was stable and unaffected by uplifts for a 

 relatively long time. This was in the Kirkfield stage before the Algonquin uplift. 



In 1894 Gilbert found that the Algonquin outlet channel does not stop at Peterboro, but 

 "continues with undiminished strength" down Trent River to the present level of Lake Ontario 

 at Trenton. The writer made the same observation in the fall of 1893, except that the channel 

 near Trenton seemed to him somewhat smaller and less capacious than that at Fenelon Falls 

 and less thoroughly scoured ; this, however, may be an error. If the old channel really extends 



i Tail-child, H. L., Glacial waters in the Lake Erie basin: Bull. New York State Mus. No. 106, 1907; Glacial waters in central New York: Bull. 

 New York State Mus. No. 129, 1909. 



2 Bull. Geol. Soc. America, vol. 21, 1910, pp. 433-434. 



s Coleman, A. P., The Iroquois beach in Ontario: Bull. Geol. Soc. America, vol. 15, 1903, pp. 357-358. 



