78 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 13, 



the bed of the Channel are as distinct as any which we estabhsh on 

 geological maps between portions of formations which differ miaeralo- 

 gicallv, — as between the lias clays and the oohtic sands which sur- 

 mount them. The mud beds forming in ninety fathom water in the 

 central trough of the Channel, are geological marls and clays ; the 

 only difference they present from one place to another being dependent 

 on the source whence the constituent particles have been deriyed. 

 On the English and Irish side of this deep area, the sea-bed is a black 

 impalpable mud, the shells of Dentalium apparently very abimdant, 

 an accumulation such as in former seas has produced beds of lias, 

 gault, or London clay. On the French side of the basin are wliite 

 and yellow marly beds of hke tenacity, and at the same depths, being 

 apparently the finer particles derived from the feldspathic rocks, 

 which the rough seas of that angle of the Channel are unceasingly 

 abrading. Under the deeper water of this central area we obtain 

 soundings of a mixed mud and finest sand, the exact counterparts of 

 beds we are famihar with in connexion with the argillaceous portions 

 of every formation, and which here seem to serve as a connectmg 

 group between areas of totally distinct mineralogical characters. 



An area which would contrast strongly with that of mud and ooze, 

 could the bed of the Channel be raised into diy land, would be that 

 of the clean siliceous sands, which would present a contuiuous extent 

 of surface equal to two-thirds of the South of England. The forma- 

 tions with which such areas as these suggest comparisons, are that 

 of Bagshot, or the lower greensands, considered in horizontal, not 

 vertical extent. 



Higher up the Channel are accumulations of sand mth coarse sub- 

 angular and rounded shingle, and largely mixed with this mass are 

 the dead shells of the larger mollusca. There exist then, even in our 

 own Channel, large areas over which materials of distinct mineralogical 

 character are being separately accumulated ; and in this respect there 

 must have been a complete identity in the operations of former times. 

 Upon this point a difficulty has been felt by many geologists, who 

 being well-aware of the additions constantly being made to the ma- 

 terials of the sea-bed, have thought it strange that soundings should 

 present such remarkable constancy as to depth. M. Brongniart and 

 others have gone so far, on this ground alone, as to draw a hne be- 

 tween the operations of present as compared mth former seas, and to 

 deny to the present seas the power of producing deposits which can 

 in any way be compared with those of geological periods. " A\Tiere- 

 ever," he says, "we have been able to ascertain the nature of the sea- 

 bed of any of the actual seas at distant times, we find it to have been 

 the same as it is now." Such is no doubt the case, though the illus- 

 trations cited by M. Brongniart are not altogether unexceptionable. 

 It may safely be admitted that in our own seas there is no variation 

 in the depth or quahty of the sea-bed. The soundings now obtained 

 agree with those laid down by Captain '^Miite ; and the French sur- 

 veyors of their western coasts confirm the same fact, in the direct 

 observations taken for the verification of their charts. The places are 

 very few where fishermen and pilots seem to think that any vertical 



