THE FLOOK OF THE OCEAN BOS WELL 277 



no less impressive than those of the continents. Moreover, the 

 employment during recent years of echo-sounding methods, so 

 economical of time and labor, has revealed interesting features 

 such as submarine canyons, deep hollows, and scarplike elevations. 

 Now that some hundred canyons have been located, Prof. R. A. Daly 

 has recently done good service by assembling the evidence relating to 

 them. He notes that several occur along the continental shelf between 

 the latitudes of Cape Cod and Cape Hatteras, including the classic 

 "Hudson River Canyon" off New York City. Thirty examples have 

 been found along Georges Bank off the New England coast and an 

 even greater number between the northern end of Vancouver Island 

 and southern California. Others have been determined off the 

 Hawaiian Islands, in the northern and western parts of the Gulf of 

 Mexico, off the western coast of Mexico, the Bahama Bank, the coasts 

 of Brazil and Ecuador, the eastern coast of Korea, both eastern and 

 western coasts of Japan, eastern and southern coasts of Formosa, off 

 the mouths of the Ganges and Indus, and the coast of Ceylon. Around 

 the African continent they have been proved to occur south of Zanzi- 

 bar, off the south coast, opposite the mouths of the Congo, Ogowe, 

 and Niger, and off the Gold Coast and Cape Verde. In Europe, they 

 have been located in the region beyond the coasts of Portugal, France, 

 and the British Isles. Thus their distribution is world-wide. Many 

 extend as cuts through the continental shelf and reach a depth of at 

 least 1,000 fathoms. Although some have no direct topographical 

 connection with great rivers (for example, those closely spaced on 

 Georges Bank), most are on the axial lines of such, notwithstanding 

 the fact that delta-building is in progress. In relation to the conti- 

 nental shelf, they usually run straight down in the direction of slope — 

 as though formed by rivers "consequent" on the shelf, their longi- 

 tudinal gradients being from 1 in 100 to 1 in 10. Some are shallow, 

 that is, not deeper than 50 fathoms (100 m) and confined to the area 

 of the shelf, but many show depths reaching from 500 to 1,600 fathoms. 

 Their walls are steep, the gradient being apparently from 1 in 3 to 

 1 in 1, and from the walls of those off California masses of fossiliferous 

 Upper Cretaceous and late Tertiary clays have been dredged. 



The mode of origin of these canyons has long been a problem — 

 indeed, ever since the time when Buchanan attributed the classic 

 example found off the mouth of the Congo to submarine river erosion. 

 Some examples have probably arisen in this way, but it seems unlikely 

 that submarine rivers can cut to great depths in relatively deep and 

 quiet oceanic waters, even if we grant Daly's postulate, that such 

 streams, being laden with mud, have increased erosive powers. Other 

 canyons are probably tectonic; that is, are due to down-folding or 



