224 Canadian Record of Science. 



the ordinary reasoning respecting the necessity of conti- 

 nental areas in the present ocean basins would actually 

 oblige us to suppose that the whole of the oceans and con- 

 tinents had repeatedly changed places. This consideration 

 opposes enormous physical difficulties to any theory of 

 alternations of the oceanic and continental areas, except 

 locally at their margins. I would, however, refer you for a 

 more full discussion of these points to the address to be de- 

 livered to-morrow by the President of the Geological 

 Section. 



But the permanence of the Atlantic depression does not 

 exclude the idea of successive submergences of the conti- 

 nental plateaus and marginal slopes, alternating with per- 

 iods of elevation, when the ocean retreated from the con- 

 tinents and contracted its limits. In this respect, the At- 

 lantic of to-day is much smaller than it was in those times 

 when it spread widely over the continental plains and 

 slopes, and much larger than it has been in times of con- 

 tinental elevation. This leads us to the further considera- 

 tion that, while the ocean-beds have been sinking, other 

 areas have been better supported, and constitute the con- 

 tinental plateaus ; and that it has been at or near the junc- 

 tions of these sinking and rising areas that the thickest de- 

 posits of detritus, the most extensive foldings, and the 

 greatest ejections of volcanic matter have occurred. There 

 has thus been a permanence of the position of the continents 

 and oceans throughout geological time, but with many 

 oscillations of these areas, producing submergences and 

 emergences of the land. In this way, we can reconcile the 

 vast vicissitudes of the continental areas in different geolo- 

 gical periods with that continuity of development from 

 north to south, and from the interiors to the margins, which 

 is so marked a feature. We have, for this reason, to formu- 

 late another apparent geological paradox, namely, that 

 while, in one sense, the continental and oceanic areas are 

 permanent, in another, they have been in continual move- 

 ment. Nor does this view exclude extension of the conti- 

 nental borders or of chains of islands beyond their present 

 limits, at certain periods ; and indeed the general principle 



