AUSTENi — TERTIARY DEPOSITS OF THE SUSSEX COAST. 61 



simply iuto this — what was the condition of the English Channel as 

 to its coast-line when certain marginal accumulations were being 

 formed ? 



If next we examine the bed of the English Channel midway be- 

 twixt Calvados and Sussex, we meet with features of outline — such 

 as lines of troughs and an advancing platform, indicative of an old 

 coast-line*: from out of the most northern of these depressions an 

 isolated mass rises nearly to the surface. The bed of the sea in this 

 part of the Channel is remarkably clean, being composed exclusively 

 of subangular shmgle. I had opportunities of examining this in 

 1854, during a calm day, and found the detritus in this portion of 

 the Channel to have been derived partly from old rooks (Silurian of 

 Normandy), and to be mixed with granitic pebbles, and some pebbles 

 of hard apparently oolitic sandstone, together with chalk-flints. 



Such a condition of seabed at such a depth (4.5-50 fathoms) in- 

 dicates subsidence ; and if we restore it to such a position relatively 

 with the present water-level as is alone compatible with the accumu- 

 lation of subangular shingle, the whole of the area to the east, which 

 has an average depth of from 25 to 30 fathoms, would be raised into 

 the condition of dry land. It is on such considerations that I am satis- 

 fied that an old coast-line may be drawn across the area of the English 

 Channel which defined its hmits in an eastern direction until some 

 time after the accumulation of the yellow boulder-clay of the Sussex 

 levels f. 



If this supposition be well founded, — and it has the support of 

 several distinct, but concurrent, sets of considerations, — the next infer- 

 ence to be drawn is this, that, inasmuch as no possible points of 

 origin for all the varied materials to be met with in the Sussex 

 accumulation are to be found around the present coast-line of the 

 Channel, their source must have been along some part of that coast- 

 line which is now submerged : the course of that coast will be in con- 

 formity with lines laid down long since, and without reference to the 

 present argument. 



Lastly, should a group of old sedimentary and crystalline rocks 

 occur in this interval, it could be easily proved, by reference to their 

 arrangement in the Department of Calvados, or it will be readily 

 seen by reference to a map, that they would agree with, because 

 they would be simply an extension of, the Normannic group. 



3. Marine Gravel above the Drift-clay. — From Aldwick to the 

 entrance to the Pagham Creek may be taken as the portion of the 

 Sussex coast along which the above-described boulder-formation, as 

 also that which overlies it, may be best seen. Very much, however, 

 depends on the quantity of shingle which may have collected along 

 the upper tide-line. 



Wherever the yellow drift-clay (fig. 4,c?, p. 49) is well exhibited, its 

 surface is invariably furrowed and uneven ; on this rests an accu- 

 mulation of coarse flint-gravel (fig. 4, c). At some places this mass 

 has no definite arrangement, but at others it passes into horizontal 



* See Map of the English Channel, Pi. XI. Quart. Journ. Geol. Soc. vol. vi. 

 t See the Map above referred to ; and especially the Map, ib. PL I. vol. xii. 



