76 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 13, 



as rippled surfaces, have been used as proofs tliat to such depths the 

 sea-bed may be disturbed by gales of wind. It may be asked, on the 

 other hand, how is it, if the oscillation of wind-wayes at certain places 

 can reach down to the bottom so as to disturb the bed, they do not 

 do so equaUy oyer those wide areas where the sea has an uniform 

 depth of that amount ? Against this too may be adduced the direct 

 and important testimony of those persons who haye worked from the 

 diyhig-apparatus, that with a fresh breeze and considerable surface- 

 moyemeut no distm'bance was eyer to be experienced below. 



Discoloration is at all times to be noticed oyer the banks in ques- 

 tion, eyen when the sea is perfectly quiescent, as far as wind-wayes 

 are concerned : we know from soundings that these places are withm 

 the range of fine sedimentary deposits ; and with respect to matter 

 falling through water slowly, we know, that at the distance of these 

 banks from any land, it will be principally in the lower strata of 

 water that the suspended matter will occm'. The tidal current which 

 has earned a column of water of 500 feet oyer a considerable space, 

 on meeting one of these banks, is suddenly reduced to 300 feet. The 

 effect of this is to produce that peculiar fomi of disturbance which 

 resembles a boihng-up and flowing-off of the surface, and which is so 

 characteristic of shoal disturbance in perfectly calm weather. By 

 this process lower strata of water are forced up, and bring with them 

 the finer particles which had reached those depths. The change in 

 the colour of the water at these places is howeyer yeiy sHght, being 

 from blue to a pale disturbed green, and the quantity of suspended 

 sohd matter by which it is produced is exceedingly small. 



§ 1. Distribution of Materials and Map of the Channel. 



As the coast-hne is the only source whence the materials which 

 compose the sea-bed are deiiyed, and as the moyement of the water, 

 at inconsiderable depths eyen in adyance of this line, is totally insufii- 

 cient to produce the fonns and conditions of the materials which oc- 

 cur there — the same also with respect to all subsequent outward 

 zones of depth — the mass fornihig the sea-bed at eyery place must 

 haye trayelled outwards. The coarser materials of seyeral areas can 

 be identified with the rocks on the coast from which they haye been 

 deriyed : thus granite and tin-stone shingle occur round the Land's 

 End and Scilly Islands, whilst the syenites and allied rocks of the 

 Channel Islands group take a wide range on that side of the Chaimel. 

 In addition to such instances as these, we haye also the eyidence from 

 the shell-sand beds, which constitute such extensiye areas in our 

 Channel, and apparently in all seas ; few if any of the shells whose 

 fragments are so abundant oyer these areas belong to them, or haye 

 Hyed there : shai-p sands, and such as can di'ift, are especially poor 

 in submarine life, nor do we meet with any weed. The great pro- 

 portion of these shelly materials has come from a contiguous higher 

 zone ; but mixed with these, and in considerable abundance, are the 

 pounded fragments of the commonest littoral species ; thus the Ha- 

 liotis tubercvlata, one of the pecuharities of the Brittany and Channel 



