200 J. D. Dana — Deep troughs of the Oceanic depression. 



New Zealand and Australia — the ocean in this area being shal- 

 low for a long distance ont on the east side and deepening to 

 2500-2700 fathoms close to that non-volcanic land, New South 

 Wales, in eastern Australia. In the Atlantic, the slope is in 

 the direction of its northeast-southwest axis, either side of the 

 Dolphin shoal, but especially the western side, rather than from 

 east to west, it commencing in the Scandinavian plateau and 

 ending in the great depths adjoining the West Indies. 



Owing to the system in the Atlantic topography, the Dol- 

 phin Shoal — the site of the Atlantis of ancient and modern 

 fable — is really an appendage to the eastern continent, that is 

 to Europe, and is shut off by wide abyssal seas from the lands to 

 the west that have been supposed to need its gravel for rock- 

 making. 



But the view that the west half of an oceanic basin is always 

 the deepest becomes checked by finding in the Indian ocean 

 that the only areas that are 3000 fathoms deep or over are in 

 the eastern part of the ocean and off the northwest coast of 

 Australia, and near western Java and Sumatra. The greatest 

 depths in its western half or toward Africa, are 2400 to 2600 

 fathoms.* 



3. Conclusions. 



1. The facts reviewed lead far away from the idea that vol- 

 canic action has been predominant in determining the position 

 of the deep-sea troughs. It has probably occasioned some 

 deep depressions within a score or two of miles of the center 

 of activity, but beyond this the great depths have probably 

 had some other origin. 



2. It is further evident that the deep-sea troughs are not a 

 result of superficial causes of trough-making. Erosion over 

 the ocean's bottom cannot excavate isolated troughs. The 

 coldest water of the ocean stands in the deep holes or troughs 

 instead of running, as the reader of Agassiz's volume has 

 learned. 



The superficial operation of weighting the earth's crust with 

 sediment, or with coral or other organic-maple limestone, and 

 filling the depressions as fast as made, much appealed to in 

 explanations of subsidence, has not produced the troughs ; for 

 filled depressions are not the kind under consideration. More- 



* In the Arctic seas, going north from the Scandinavian plateau, the water 

 deepens north of the latitude of Iceland, between Greenland and Spitzbergen, to 

 2000 fathoms, and farther north to 2650 fathoms, m the latitude nearly of Green- 

 wich ; and it is probable that the 2000-fathom area extends over the region of the 

 North Pole. The continents of Europe (with Asia probably) and North America, 

 are proved by the shallow soundings over the adjoining Arctic seas and the islands 

 or emerged land, to extend to about 82^° N., which is about 450 miles from the 

 pole. 



