44 ON CHANGES IN THE DISPOSITION 



porting the submarine alluvia, and in modifying their 

 forms. The changes which these undergo are well 

 known to mariners ; as is their gradual increase, from 

 the accession of materials ; whence it is, that after the 

 lapse of a few years, they require fresh soundings and 

 buoys, especially in" such narrow channels as our own. 

 It is easy to understand how the deposition of mud and 

 sand may be determined by peculiar forms in the land, 

 producing a state of comparative repose at some point ; 

 or^through an eddy, from the combination of such forms 

 with the tides. Thus is the Dogger Bank determined 

 by the meeting of these, as is that off Cape Rath, and 

 those in the Irish Channel. The Great Bank of New- 

 foundland is the produce of the Gulf stream ; as those 

 off the mouth of the Baltic are produced by the cur- 

 rent flowing out of this confined sea. 



The greater movements of the ocean appear to be the 

 leading causes of the distribution of submarine alluvia. 

 It is ,now known to include a system of established cur- 

 rents, mutually connected and permanent. Their im- 

 portant services in equalizing its temperature belong to 

 another department of natural philosophy ; but they 

 seem not less to interest the geologist, by producing the 

 effects under review. I may refer to Rennel for the de- 

 tails of that great current which, traced from the East- 

 ern Coast of Africa, passes the Cape of Good Hope 

 into the great ocean, proceeding to the North-west 

 along the African shore, with a breadth which exceeds 

 a thousand miles near the parallel of St. Helena : 

 whence, joining one from the North, they unite and turn 

 to the South-west, upon the American Coast. Meeting 

 at Cape St.Roque with another running northwards, it 

 falls into the Gulf of Florida, producing the gulf stream, 

 which running northward, at length stretches across to 

 Britain, depositing on our islands the buoyant produce 



