17S Chalmers — Shore Lines of the St. Lawrence Valley. 



with apparently the same correlative uplifts to the east and to 

 the west, when on reaching the level of the 775-705 feet shore 

 line in the basin of the Great Lakes there was another halt. 

 This shore line is also recorded in the St. Lawrence Yalley, 

 though now shown at various altitudes and in various posi- 

 tions. The two higher strands north of Ontario and Erie 

 Lakes then became slightly tilted towards the northeast. 



3. Another downward movement of the central axis follow- 

 ing, the formation of the " Iroquois beach " took place on the 

 one hand, and corresponding shore lines at low levels in 

 the St. Lawrence Yalley on the other. The upper shore lines, 

 both on the east and west of the central oscillating axis, would 

 now slope towards it, though they have since returned nearly 

 to a horizontal attitude. 



4. Following was a period of moderate oscillations along the 

 axis referred to, some downward and some upward, the forces 

 producing them having apparently been largely spent, or hav- 

 ing approached an equilibrium. These changes resulted in 

 the breaking down of the strands along the margin of the 

 oscillating zone on both sides, and in a considerable amount of 

 denudation taking place. Lake Ontario was probably lower 

 than at present, perhaps nearly or quite at sea level. 



5. A slow series of reverse movements then set in which 

 consisted mainly in a rise of the crystalline axis. This has 

 continued to the present day with correlative subsidences in 

 the areas formerly uplifted to the east and west. These 

 changes are evidenced by the fact that the " Iroquois beach," 

 which was, just previous to this period, in a horizontal atti- 

 tude, is now tilted to the southwest, and similar movements, 

 though in a reverse direction, have taken place in the St. 

 Lawrence Yalley, the raised shore lines there now sloping east- 

 ward longitudinally. What the amount of the uplift at the 

 Thousand Islands has been since, it is difficult to say. Judg- 

 ing from the present levels of the " Iroquois beach " it would 

 seem as if the rise must be fully 200 feet ; but the hinge or 

 axis of the movement may not have been at the eastern end of 

 the existing beach. 



The oscillatory movements of the barrier referred to would 

 seem to have been limited and slow, nevertheless they affected, 

 it appears, not only the granite axis, but a wide tract of 

 country on either side, beyond which, as shown, complementary 

 movements occurred. Even when the axis was at its lowest 

 level, however, Lake Ontario must have been somewhat higher 

 than the sea or gulf ; for there is evidence of an eastward flow 

 of the lake waters at this stage. Stratified beds of gravel and 

 sand showing deposition in waters flowing in the direction 

 indicated were found upon the granite axis at altitudes of 800 



