AUSTEN — TERTIARY DEPOSITS OF THE SUSSEX COAST. 43 



The lower nummulitic strata near the entrance to Pagham Creek 

 present conditions of deposition which deserve notice : between the 

 beds of compact sand are numerous large root-like bodies, which 

 spread over each surface ; the beds themselves contain in abundance 

 the casts of bivalve shells, all placed as when living, whilst at inter- 

 vals are lines of rounded bodies, which consist of clay formed mto 

 pebbles, as may be observed now along the margins of lakes, ponds, 

 or estuaries, and which are produced by the ripple of the water where 

 it breaks gently along a marginal line. 



Coarse detritus, such as rounded and subangular shingle, is not 

 uncommon in other parts of the lower nummulitic series ; it consists 

 wholly of chalk-flints. 



French Coast. 



Somme. — The land bordering on the east end of the Channel need 

 not be described in any detail, inasmuch as it consists mainly of second- 

 ary strata. The littoral deposits of the Somme Department have not 

 been surveyed or described so as to supply us with any very definite 

 details as to the deposits of the low levels, which, from Etaples, occupy 

 a considerable breadth southwards. The valleys of the Canche, the 

 Authie and the Somme, which have their steep sides on the south- 

 west, are all parallel with the axis of Artois, and are probably referable 

 to lines of fracture. The lower portions of these valleys contain sub- 

 aerial and alluvial accumulations, which include abundantly the remains 

 of large mammalia, associated with laud and freshwater shells of 

 existing local species. 



At the mouths of the Canche and the Somme there are moreover 

 indications of a small change of level of recent date : this change has 

 somewhat complicated the geological phaenomena of these valleys : 

 the sequence on the whole will be found, however, to correspond 

 with the upper part of that on our own Sussex coast. 



Seine Tnfcrieure. — Along the rest of the coast of Upper Normandy, 

 the sea now reaches the base of the vertical chalk-cliffs * which are 

 continued with a uniform height as far as Cape Antifer. Perhaps 

 one of the most striking features of the Channel coast is this lofty 

 wall of dazzling white chalk, when seen from a short distance in the 

 offing. The district which extends inland from this part of the coast 

 is overlaid, though not uniformly, by an accumulation of clayey 

 gravel, containing flints much broken, but not worn. I am not 

 aware that any true tertiary strata occur over this surface, at least 

 on the coast-section, till near Treport ; here, and again beyond 

 Dieppe, are the well-known fluvio-marine beds of the nummulitic 

 formation, corresponding with those at Newhaven, but wliich are 

 here surmounted by a marine deposit of dark sandy clayf. These 

 beds seem to owe their preservation to their having been accu- 

 mulated in an old depression of the chalk, for the process has been 

 one of filling up — the higher beds overlapping the lower. The upper 

 surface here presents just the same uniform level as does the rest 

 of the coast, and the only peculiarity to be noticed with respect to 



* Quart. Journ. Geol. Soc. vol. xi. p. 118. 



t Prestwich, Quart. Journ. Geol. Soc. vol. xi. p. 230. 



