DEPTHS AND DEPOSITS OF THE OCEAN 195 



present state of our knowledge, is shown in Map HI. On Depths of 



the Nortt 

 Atlantic. 



this chart the soundings in depths greater than 1000 fathoms '"^^ ^"""^^ 



are indicated by the hrst two figures, and they show that the 

 North Atlantic is now well sounded — in fact, probably the 

 best sounded of all the ocean basins. The recent soundings 

 by the "Michael Sars " did not bring to light many new facts 

 as to depth, and it is not likely that any great changes in the 

 contour-lines will be revealed by future soundings, though it is 

 possible that further submarine cones, like the Seine Bank and 

 Dacia Bank and the Coral Patch, may yet be discovered. 



A comparison of this map with the depth map published by Maury's 

 Maury in 1854, which is reproduced in Map I., brings out ^^P'^^ "^^p- 

 at a glance the strides that have been made in our knowledge 

 regarding the depth of the North Atlantic since that time — 

 a progress from comparative simplicity to great complexity. 

 Maury's 4000 -fathoms area in the North - West Atlantic, 

 based upon some doubtful soundings (two of them exceeding 

 5000 fathoms and another in 6600 fathoms), has disappeared, 

 though the existence of very deep water in the neighbourhood 

 is evidenced by the soundings in the Suhm Deep. These deep 

 soundings laid down by Maury were among the early attempts 

 at deep-sea sounding, and the records of such depths as 6600 

 fathoms, no bottom, were due to the uncertainty as to when 

 the sounding-tube touched bottom. The only part of the 

 North Atlantic where the depth is now known to exceed 4000 

 fathoms (in the Nares Deep north of the West Indies) is 

 blank on Maury's map, but the northern portion of the mid- 

 Atlantic ridge, on which the Azores plateau is situated, is 

 correctly indicated, though since modified in outline ; the 

 continuation southward of this ridge was, however, unknown 

 in Maury's time. 



Reference has already been made to the relatively large area 

 occupied throughout the world by the continental shelf, which 

 is equal to about 7 per cent of the entire ocean-floor. The 

 continental shelf apparently attains its maximum development Continental 

 in the North Atlantic basin, if we include the tributary seas J^J[i;" ^^^ 

 (x^rctic Ocean, Mediterranean, etc.). The total area of this Atlantic, 

 basin may be estimated at about 23 million square miles, and of 

 this area no less than about 6 million square miles (or 26 per 

 cent) lies between the shore-line and the lOO-fathoms line. 

 While the gentle gradients of the continental shelf cover such Continental 

 an extensive area, the continental slope beyond the lOO-fathoms ^T°PtV" * " 

 line seems, on the other hand, to be relatively very steep, for Ati 



in the 



th 

 antic. 



