A REMARKABLE SEA. 



131 



its limits, where this depth is greatly exceeded. One lies 

 at the foot of the range of mountains above mentioned ; 

 another at the base of the immense submarine ridge, of 

 which the Cayman Islands form tiny aerial summits ; 

 and another immediately to the south of the Mysteriosa 

 Bank. In all these localities, the depth of water attains 

 to eighteen thousand feet; while just about ten miles to 

 the north of Swan Island, there is another long and narrow 

 canyon over one hundred and fifty miles in length, where 

 the abysmal depth of twenty thousand feet is reached. 



For a sea, as compared with an ocean, these figures are 

 very remarkable : the very greatest depths discovered in 

 the Atlantic, in one extremely limited area to the north of 

 Puerto Rico, being for instance 27,366 feet — an appalling 

 abyss. Twenty thousand feet is equivalent to three- 

 and-three -quarter miles ; but to realize fully what a depth 

 like this means, one requires to have some other facts by 

 way of comparison. Thus we might state, that in no part 

 of the English or Irish Channel, or of the North Sea, does 

 the depth exceed six hundred feet ; and that in passing 

 across the latter sea from the Wash to Holland, there 

 would never be a greater depth than sixty feet beneath 

 one. This, of course, is to quote extreme cases, but they 

 are at least bases for comparison. 



Perhaps a better way would be to imagine ourselves 

 once more standing upon Swan Island, and the entire 

 Honduran Sea drained of its water. We have already 

 seen that Swan Island rests upon a bank, which is roughly 

 ten miles long by four miles wide, and that the depth 

 of water very gradually increases, from about five fathoms 

 in the immediate neighbourhood of the island, to some- 

 thing like thirteen fathoms on the edge of the bank. 



If, therefore, we imagine ourselves leaving the island 

 and setting oat to walk in a northerly direction ; we should, 

 for roughly two miles, proceed down a hardly perceptible 

 slope, strewn with clumps of coral rock, and coated with 

 coral sand and coral mud : until we suddenly found 

 ourselves at a point where the ground fell rapidly away, 



