1849.] AUSTEN ON THE VALLEY OF THE ENGLISH CHANNEL. 81 



But even here, in proportion as one part of the formation affords in- 

 dications of greater depth than the rest, as between the chalk marl 

 and upper chalk, so stratification becomes less distinctly marked : 

 the deep sea mud-beds, such as the old slate rocks in their original 

 condition, the London and other great clay groups, are not stratified, 

 but only laminated. Lines of stratification are obviously due to an 

 interference from time to time in the process of horizontal deposition, 

 but as to the cause in this particular case I am unable to offer any 

 conjecture, nor can I meet with one. 



In a sea where accumulation goes on by an outward distribution 

 of materials, there will be an obvious tendency to form banks and 

 terraces. The termination of the sands over the mud-bottoms are of 

 this character, and such are also the accumulations of a higher zone 

 which surround the deep pits between the coasts of France and those 

 of the south-west of England. 



In order to realize the geological bearings of such processes as we 

 have here considered, we have only to imagine a long valley formed 

 by subsidence or otherwise, to be so placed that the waters of an ad- 

 jacent sea should flow in and occupy it to the depth of 100 fathoms. 

 The nature of its action would be as follows : The products of wave 

 destruction along the coast-line would be carried outwards and ar- 

 ranged in zones according to states of comminution and specific gra- 

 vities ; simultaneous accumulation of all these various conditions of 

 detritus would take place, and if followed from the coast-line outwards 

 would present a gradual change from one mineral character to another. 

 By lapse of time and process of accumulation, the bed of such an area 

 would be raised, the depth of water diminished ; sands would then 

 be carried out where silt and ooze had been deposited at first, and 

 beds of coarse materials would occupy the zones of finer sands. The 

 accumulations from either side might thus be brought up, till a large 

 portion of the area would have the kind of sea-bed known as coarse- 

 ground. When the higher portions of such channel no longer offered 

 any places for the finer sediment, it would travel outwards, or towards 

 the opening and lower portion of such depression ; and the whole of 

 such an area would bear the same relation to the wider ocean with 

 which it communicated, that its own river estuaries bore to itself. 

 Such is the actual relation of the English Channel to the Atlantic 

 Ocean : it is the estuary of the rivers of a portion of Western Europe, 

 in which are repeated on a wider scale all the phaenomena of tidal 

 action which minor estuaries exhibit. 



In the case here imagined, we have assumed a given area or valley of 

 depression, modified afterwards by the process of accumulation alone ; 

 the whole of the process would be conducted along a very narrow zone 

 of breadth compared with the extent of the sea, whenever the sea was 

 an open one, and for all geological purposes such lines of section will 

 perhaps be safer guides than those taken in close seas. In our own 

 Channel, as we shall see, the area of sedimentary deposits is bounded 

 on the west by the barrier which separates it from the great valley of 

 the Atlantic : the distance of the deep sea mud from Cape Clear south 

 is about the same as that of the same deposit from the Scilly Isles, 



VOL. VI. PART I. G 



