ABSTRACTS AND DISCUSSIONS OF PAPERS 79 



scribed, in the channel just beyond the end of the gorge. This shows that the 

 level in Lake Ontario was, after the birth of the falls, even lower than I had 

 previously announced. 



These are new facts leading to further precision, besides confirming earlier 

 results. 



Presented in abstract extemporaneously. 



TERRESTRIAL STABILITY OF THE GREAT LAKE REGION 

 BY J. W. SPENCER 



(Abstract) 



■ Among the results obtained by studying the lower lake terraces is one relat- 

 ing to the cessation of earth-movements. The terraces in question are those 

 most strongly developed at or near the mouths of tributary streams, recurring 

 all the way from the head of the lake to below the outlet of Lake Ontario, at 

 12 to 20 feet and 2 to 5 feet above its level. In them no deformation is deter- 

 minable, in contrast with the differential movement of 540 feet between the 

 head of the lake and Parishville, New York, as seen in the Iroquois beach, 

 with tilting varying from 2 to 6 feet per mile. Having previously proved from 

 the daily fluctuations of lake levels that there has been absolutely no earth- 

 movement since 1854, these terrace features show that the cessation dates back 

 a long time. The movements were in operation after the diversion of the 

 Huron drainage to that of Lake Erie, which I have placed at 3,500 to 4,000 

 years ago. At present this would give near the date for their cessation. 



Presented in abstract extemporaneously. 



SCOUR OF THE SAINT LAWRENCE RIVER AND LOWERING OF LAKE ONTARIO 



BY J. W. SPENCER 



( Abstract) 



I am not aware of previous investigations on this problem. When the waters 

 of the Ontario basin were subsiding from the earlier glacial lake, the Saint 

 Lawrence River channel did not come into existence until they fell to a level 

 of not more than 20 feet above the present stage. This figure represents the 

 total lowering of the lake due to the river scour acting on its general bed of 

 drift. At the upper rapids the river has exposed very little rock. Thus at the 

 first, or Gallops Rapids, the river flows over beds of boulders in two of its 

 branches, while in the third the rock has been channeled for only a quarter of 

 a mile (in Ordovician strata). These features show the relative youthfulness 

 of the modern Saint Lawrence River. The present shoreline of the lake was 

 examined for evidence of deformation, but neither in it nor the lower terraces 

 could such be found. 



To one who had primarily observed the coast of the lake at Hamilton and 

 Toronto, where great beaches occur, he would be surprised to find how wide- 

 spread has been the cutting away of the shores or the small development of 

 the beach. It is much less developed than the Iroquois. Tndeed, the interven- 

 VII— Bull. Gbol. Soc. Am., Vol. 27, 1915 



