DILUVIUM. 277 



Brighton is situated on an immense accumulation of water-worn ma- 

 terials, which fills up a valley, or hollow, in the chalk. This diluvial de- 

 })osit is bounded on the north-west by the South Downs ; on the east it 

 extends to Kottingdean, and is there terminated by the chalk; on the 

 south it is washed by the sea, and forms a hue of cliffs from 70 to 80 feet 

 high ; these exhibit a vertical section of the strata, and enable us to ascer- 

 tain their nature and position. 



A vertical section of the chffs, about half a mile east of Brighton, is 

 represented in Tab. iv. fig. 1. The lowermost bed is 



1. The Upper, or flinty chalk; which constitutes about six or eight 

 feet of the lower part of the cliff, and dipping southward, extends to an 

 unknown distance into the sea. The continuation of the chalk behind 

 the calcareous bed is marked ^^ former cliff" in the sketch; and is in- 

 troduced to shew the relative situation of the masses, but without any 

 regard to pi'oportion. 



2. Bed of fine sand, from three to four feet. 



3. Shingle bed, from five to eight feet. 



4. Calcareous bed, formed of the ruin of the chalk strata, with an in- 

 termixture of clay; it is provincially termed Coombe rock; — from 50 to 

 60 feet. 



The chalk presents its usual characters; and in various parts of its 

 course is traversed by vertical and obHque veins of flint. 



The sand is very fine, varying from pure white to a light reddish 

 brown colour. It disappears about a mile to the east of Brighton, where 

 the succeeding deposit lies immediately upon the surface of the chalk. 



The shingle bed consists of pebbles, formed, Uke the present beach, of 

 broken chalk flints rounded by attrition. It contains also water-worn 

 blocks of granite, porphyry, slate, limestone, and druid sandstone. It oc- 

 casionally envelopes masses of broken shells. The upper part of this bed 

 is cemented together by calcareous spar, of a hght yellow or amber colour, 

 forming a kind of breccia of a very singular appearance*. 



* A specimen of this mineral is figured in Sffwerbys British Mineralogy. 



