WEST INDIES. 
267 
instance, the Misteriosa Bank, on the edges of which the 
soundings change in 250 fathoms horizontal distance, from 
11 to 210 fathoms ; off the northern point of Old Provi- 
dence Bank, in 200 fathoms horizontal distance, the change 
is from 19 to 152 fathoms ; off the Great Bahama Bank, in 
160 fathoms horizontal distance, the inclination is in many 
places from 10 fathoms to no bottom with 190 fathoms. 
In all parts of the world, where sediment is accumulat- 
ing, something of the same kind may be observed ; the 
banks shelving very gently far out to sea, and then termin- 
ating abruptly. The form and composition of the banks in 
the middle parts of W. Indian sea, clearly show that their 
origin must be chiefly attributed to the accumulation of 
sediment ; and the only obvious explanation of their iso- 
lated position is the presence of a nucleus, round which 
the currents have collected fine drift matter. Any one who 
will compare the bank surrounding the hilly island of Old 
Providence, with the banks in its neighbourhood which 
stand isolated, will scarcely doubt that they surround sub- 
merged mountains. We are led to the same conclusion by 
examining the bank called Thunder Knoll, which is separ- 
ated from the Great Mosquito bank by a channel only seven 
miles wide, and 145 fathoms deep. There cannot be any 
doubt that the Mosquito bank has been formed by the ac- 
cumulation of sediment round the promontory of the same 
name ; and Thunder Knoll resembles the Mosquito bank, 
in the state of its surface submerged 20 fathoms, in the in- 
clination of its sides, in composition, and in every other 
respect. I may observe, although the remark is here irre- 
levant, that geologists should be cautious in concluding that 
all the outlyers of any formation have once been connected 
together, for we here see that deposits, doubtless of exactly 
the same nature, may be deposited with large valley-like 
spaces between them. 
Linear coral-reefs and small knolls project from many 
