554 KIRTLEY F. MATHER 



SUMMARY 



Withdrawal from the Thousand Island region of the Labradorian 

 ice barrier responsible for the existence of Lake Iroquois was fol- 

 lowed by accumulation of fluvio-glacial gravels in Napanee Valley. 

 The pro-glacial stream descended to a locality which is now less 

 than 325 feet above sea-level before it debouched into Gilbert 

 Gulf, an arm of the Champlain Sea. At the same time Algonquin 

 River carried the overflow from Lake Algonquin down Trent 

 Valley past Trenton, Ontario, to an outlet which is now beneath the 

 waters of Lake Ontario. 



The melting-back of the ice front from Covey Hill toward the 

 Height of Land was contemporaneous with a positive movement of 

 the strand-line which carried marine waters toward the head of the 

 Ontario basin and drowned the Napanee and Trent valleys. The 

 positive movement of the strand-line was followed by a negative 

 movement, which began approximately at the time of complete 

 disappearance of Labradorian ice and has continued nearly or 

 quite to the present time. 



Disregarding crustal movement, the waning of Pleistocene ice 

 caps would result in a world-wide transgression of the sea as its 

 volume was increased by the return of water temporarily abstracted 

 to form the ice masses. In high latitudes the amount of movement 

 of sea-level would be much less than in low, because of gravitative 

 attraction of the ice, but everywhere the direction of movement 

 would be the same. 



Secular adjustment following removal of ice load was delayed 

 in the Ontario-St. Lawrence region long enough to permit a stage 

 of sea-advance before upward tilting overcame the effect of ice- 

 melting and the stage of sea-retreat was reached. 



