IL 



Are Great Ocean Depths Permanent ? 



IT has been suggested by the editor that EngHsh readers would like 

 to hear my views on that much-debated question, the Perma- 

 nence of Ocean Basins. I am rather at a loss how to deal with the 

 subject, because this question involves so many difficult chapters 

 in the history of our planet, and because I regret to see that discre- 

 pancy of views exists on fundamental principles. 



Mr. Wallace begins by arguing from the principle that "on 

 any large scale, elevation and subsidence must nearly balance each 

 other, and thus, in order that any area of continental magnitude 

 should rise from the ocean floor, .... some corresponding area 

 must sink to a like amount." I venture with deference to reply that I 

 cannot agree to this. It seems, on the contrary, as if two different 

 types of movement had been going on since the first formation of the 

 terrestrial crust. In the first place, there is folding, recently explained 

 in a masterly way by Professor Lapworth, in his Address to the 

 British Association. Secondly, there is the sagging-down or " eflfon- 

 drement " of smaller or greater parts of the crust, caused by the 

 progressive diminution of the planet's radius. This descent of parts of 

 the earth's crust seems to he the true origin of the great oceanic basins. 



Sometimes the contour of the sunken area follows the trend of a 

 folded mountain chain ; at another time it may cut right across it. 

 In smaller examples the outline very often takes a more or less irregu- 

 larly circular or elliptical form. The descent of a considerable area, 

 forming a large new depression, demands a certain part of the existing 

 \olume of oceanic waters for the filling of the new depth. The 

 consequence is the sinking of the oceanic surface all over the planet, 

 and the apparent step-like rising of coast lines. Thus is explained the 

 apparently episodic elevation of whole continents, without any 

 disturbance of horizontality, or the least alteration of the net of 

 watercourses spread over the land. It is in this sense alone that a 

 certain balance of " elevation " and " subsidence " might be conceded. 



In the entire Pacific region the limits of the oceanic basin are 

 traced out by the trend of long mountain folds. So it is from New 

 Zealand and New Caledonia to the borders of Eastern Asia, to the 

 Aleutians, and all along the western coast of both Americas. This is 

 not the case in the Atlantic, nor in the Indian Ocean ; here the 



