1849.] AUSTEN ON THE VALLEY OF THE ENGLISH CHANNEL. 79 



accumulation or depression is taking place — any at least of a perma- 

 nent character ; and the reason of it is, that accumulation does not 

 take place in this direction, but according to a process of outward 

 distribution already alluded to. The materials of the sea-bed are in 

 equilibrium with the moving power of the water at every place ; the 

 sediment of the ninety fathoms' depths could not remain between the 

 mainland and Alderney for a single tide. Should any extraordinary 

 action of the sea, such as that of a continued gale and high tides, 

 produce along the submarginal zone a deeper disturbance than usual, 

 the common effect is, that an accumulation of sea-bed is brought up 

 from such deeper zone and thrown down on a shallower one : such a 

 disturbance is not unusual, but the effect is not permanent ; such ma- 

 terials being within the ordinary moving power of the sea in their new 

 place, are soon carried away * . In the course of last summer I received 

 some curious information respecting the formation of such temporary 

 banks, from men engaged in the oyster fisheries on the French coasts. 

 It seems that with a continued gale from the west, large areas of their 

 dredging-grounds become at times completely covered up by beds of 

 fine marly sand, such as occurs in the offing, and which becomes so 

 compact and hard, that the dredge and sounding-lead make no im- 

 pression on it : with the return of the sea to its usual condition, a 

 few tides suffice to remove these accumulations. 



§ 2. The large areas of uniform sea-bed, wherever there are long 

 lines of uniform depth, are the ob\ious results of the laws which we 

 have seen determine the quality and distribution of submarine ma- 

 terials. The termination of deposits of a well-defined character, such 

 as the shell-gravel beds or those of clean sand, is often by slopes more 

 or less steep ; the two conditions taken together point clearly to the 

 mode of accumulation. If we take the great sand plain, the particles 

 brought down are drifted on over the horizontal surface, till they 

 reach the edge of that quality of sea-bed or soundings ; they then 

 fall over the slope, and are beyond the reach of the combined action 

 which has moved them along : it is only therefore in advance of each 

 area of definite character that the materials belonging to it are ulti- 

 mately deposited. It is this process which has produced that dia- 

 gonal arrangement to be observed in so many deposits from the crag 

 to old red sandstone. The red crag shows us instances of the coarse- 

 ground sea-zone, the coralline crag of the region of shell-sand. A 

 modification of this arrangement is presented by these two groups ; 

 in the red crag we meet with a structure which may be called torren- 

 tial, by an apphcation of M. Necker's term ; with this we m.eet with 

 constant instances of the partial removal of the upper portions of 

 subordinate beds, subsequent to their accumulation : with the coral- 



* The Schole bank rises out of twenty to twenty-five fathoms water. In 1824, 

 Captain M. White describes it as having steep sides and covered with only seven 

 and a half feet of water. He surveyed it again in 1831, and found it much in- 

 creased in size, with regular soundings about it. In 1833 the French surveyors 

 found it much in the condition in which Captain White first described it. Such 

 an instance as this indicates only rapid accumulation for a few years, followed by 

 as rapid removal. There are many cases of hke character, but they all belong to 

 the submarginal zone at most, and to this very rocky part of the Channel sea -bed. 



