48 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



This upper gravel-terrace has a very marked slope or face along its 

 southern edge. 



The second level is that which extends from the base of the upper 

 terrace ; it is also composed of gravel, and may be seen in numerous 

 excavations about Chichester, as over the Port-field, and eastwards, 

 along the line of railway. This gravel is much more worn than the 

 other, is cleaner, and has a very marked horizontal arrangement, with 

 seams of diagonally drifted sands. It thickens rapidly from north to 

 south, or seawards. 



In places where these latter gravel-beds are worked through, as 

 along or near the line where they meet those first described, the 

 relative positions of the two accumulations may be seen, the lower 

 beds of the red gravel being continued beneath the second or lower- 

 level series. The gravel-beds of the south of Sussex may therefore 

 be divided into two groups, distinguishable by colour, composition, and 

 relative position; the oldest is locally known as the "red gravel," 

 and the newer as the "white gravel." 



The beds of red gravel, of which a portion alone now remains, at 

 one time extended over the whole of the chalk and nummulitic plat- 

 form which supports the deposits of the Sussex levels and patches 

 of it may be seen in advance of the present coast-line as far as low 

 water (see fig. 4,/, p. 49). The line of slope which marks their 

 westward boundary is nothing more than the coast-line of the period 

 of the " white gravel" series. The materials of the one have been 

 taken from the other accumulation, and re-arranged. 



In addition to chalk-flints, the "red gravel" contains blocks of 

 grey-wether-sandstone from the lower tertiary strata ; but no animal 

 remains have ever been found ; in which respect, notwithstanding 

 its low position, it resembles the gravel-beds of the higher-level 

 gravels on the chalk, and to that series I am disposed to refer it. 



§ III. Deposits of the Sussex Levels, above the Red Gravel. 



1 . Marine Deposits with Lutraria rugosa. — The oldest of the newer 

 tertiary deposits of the Sussex levels, taking the series in ascending 

 order, is to be seen only at extreme low-water in Bracklesham Bay, 

 thence round or in advance of Selsea Bill, as far as the entrance into 

 Pagham Harbour ; it has been met with beneath the overlying deposits 

 of the Selsea peninsula at a depth which places its upper surface below 

 the high-water-level there, and the consequence of this position is, that 

 it is only occasionally and imperfectly exhibited ; towards the upper 

 limit of the tide it is generally covered up by sand and shingle ; lower 

 down it is presented in detached patches. 



This portion of the Sussex series forms the "mud-deposit" of Mr. 

 Dixon's description, — a very fitting name, as, apart from other con- 

 siderations, its composition distinguishes it from the beds above ; it 

 consists of an extremely fine sandy mud, which is so firm and cohe- 

 rent that even small patches resist the action of the sea for a con- 

 siderable time ; but for this, it would be rapidly removed from off 



