APPENDIX. 253 



distance, from 11 to 210 fathoms; off the northern point 

 of the bank of Old Providence, 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. On coasts in all parts of the 

 world, where sediment is accumulating, something of this 

 kind may be observed ; the banks shelve very gently far out 

 to sea, and then terminate abruptly. The form and com- 

 position of the banks standing in the middle parts of the 

 W. Indian Sea, clearly show that their origin must be 

 chiefly attributed to the accumulation of sediment ; and the 

 only obvious explanation of their isolated position is the 

 presence of a nucleus, round which the currents have 

 collected fine drift matter. Any" one who will compare the 

 character of the bank surrounding the hilly island of Old 

 Providence, with those 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 

 separated 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 accumulation of sediment round the pro- 

 montory of the same name ; and Thunder Knoll resembles 

 the Mosquito Bank, in the state of its surface submerged 

 twenty fathoms, in the inclinations of its sides, in com- 

 position, and in every other respect. I may observe, 

 although the remark is here irrelevant, 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. 



