18 



resting upon the foundation of chalk, and following this to the 

 east we find the old beach suddenly ends against the ancient 

 sea-cliff which here nearly turns at right angles to the present 

 cliff. At Black Rock there is an interesting occurrence of a 

 fallen mass of chalk in the old beach. Tracing the old beach to 

 the west of Brighton, through Hove to Portslade, the level 

 gradually widens and the old sea-cliff recedes, until at Aldrington 

 and Old Portslade the chalk cliff is a mile or so inland. 



The recent excavations by the shore at Aldrington, where 

 sand pits have been opened in the Raised Beach, have given 

 geologists a good opportunity for examining these beds in detail. 



By comparing these cliff exposures on the east and west of 

 Brighton we can see that they are situated in different parts of 

 the same bay, for at Aldrington the Raised Beach consists of 

 1 6ft of sand followed by about 6in. of pebbles; whilst at Black 

 Rock we have only a few inches of sand, but about loft. of large 

 boulders and rounded pebbles. Aldrington, in fact, stands on 

 that part of the bay which at the time of the formation of the 

 Raised Beach was a mile or so from the shore-line. This is 

 further proved by the section at the lirick pit near Portslade 

 Station, where there is very little sand and 3ft. of beach pebbles. 



In the sand bed at Aldrington marine shells are very com- 

 mon, chiefly the obtuse periwinkle {Littoj-ina obtusata) and the 

 mussel {Mytilus edulia). Both of these are found in shallow 

 water, and prefer areas between high and low tides. The mussel 

 shells are extremely fragile. \\\ this case it appears to be 

 due to the following cause. The shell consists of an inner 

 nacreous and an outer fibrous layer. The nacreous portion 

 which was of aragonite, has changed over into the stable 

 condition of calcite, and in the process rough cleavage cracks 

 were developed which has tended to make the shell rotten. A 

 large subangular flint with many barnacles attached was found 

 in the sand at this locality. 



The white sand contains innumerable microzoa. Of the 

 O.stracoda, the little bivalved Crustaceans, the species which lived 

 during the accumulation of the .sand of the Raised Beach are 

 those which we find near the shore at the present day, with 

 the exception of two forms which are more northern in their 

 habitat. Six species of the genus Cy there were found here. 



The carapaces of eight species of Ostracoda, which are known 

 to live only in streams, ponds, and marshes, were found intro- 

 duced into the sand of the Raised Beach, by fluviatile or even 

 aeolian agency. 



A derived fossil microzoic fauna is also present, which is 

 made up as follows : — 



Two species of Wealden Ostracoda, which were probably 

 introduced into the Raised Beach by a river draining the Weald, 

 as the river Adur. 



