270 THE CANADLAN NATURALIST. [V^ol. X. 



As an evidence of local oscillation, Mr. Gilbert has pointed 

 out that the Irondequoit Bay, near Rochester, was excavated to 

 the depth of more than 70 feet, and two miles wide, by streams 

 of Post-glacial (or Inter-glacial) date, and subsequently submer- 

 ged to the above depth. From this, his conclusion is that at the 

 time of the excavation of this fiord-valley, the relative altitudes 

 of the locality and the rock-sill over which Lake Ontario dis- 

 charges differed from their present status by more than 70 feet. 

 Corresponding perfectly with Irondequoit Bay is Burlington Bay 

 at Hamilton, with a depth of 78 feet, with a closed beach across 

 its mouth. From this and other local features, the surface geol- 

 ogy of the Dundas valley would indicate a greater elevation, to 

 the extent of more than 78 feet at the head than at the present 

 outlet of the lake. 



Let us consider for a moment the physical effect that would be 

 produced upon the stratification by the subsidence of the north- 

 eastern portion of Lake Ontario and the upper St. Lawrence. 

 The dip of the rocks at the western end of Lake Ontario is 

 about 25 feet in a mile, westward of south. At the eastern end 

 of the lake, I believe, it is somewhat greater. The deeper por- 

 tions of the lake are more than 40 miles from its present outlet. 

 Any local depression gradually extending north-eastward from 

 the deepest soundings of the lake, to even the extent of 25 feet in 

 the mile, would lower the outlet by the St. Lawrence to an ex- 

 tent far greater than would be necessary to drain the lake, pro- 

 vided this change took place at a time of high continental eleva- 

 tion, thus producing a broad depressed valley. We know that 

 the valley of the lower St. Lawrence is submerged to the depth 

 of at least nearly 1200 feet. The rocky boundaries of the region 

 could scarcely more than indicate this change of level as the dip 

 of the rocks would pass from the condition of 25 feet in the mile 

 or less to almost absolute horizontality, and we have no means of 

 comparison. If, however, the elevations took place to the north- 

 ward to a greater extent then the southward, such as might be 

 occasioned by a change of the centre of gravity of the earth, then 

 the region to the southward of the lakes might be relatively 

 sufficiently lowered as to permit a portion of the drainage to pass 

 out by either the Mohawk or Seneca Lake valleys, which 

 evidently during some portion of the Ice Age discharged waters 

 from the expanded basin of the lake. The local oscillations would 

 also be necessary in the explanation of the complete closing of 



