PLASTIC CLAY. 
.•53 
very beautiful. Teeth and bones of tishes are also 
found. 
PLASTIC CLAY. 
In conformity with the nomenclature of MM. 
Cuvier and Brongniart, a j)rinci])al division of the 
tertiary formations, consisting of various beds of 
sand, clay, marl, and gravel, is distinguished by 
the name of Plastic Clay (^Ar^ille J^lnsfique^. An 
attentive examination of the general points of re- 
semblance in the physical characters, and organic 
remains, of these irregular alternations above the 
chalk, leaves no doubt of their being members of 
a series of nearly contemporaneous depositions, 
intermediate between that formation and the Lon- 
don clay ; but the propriety of the separation of 
these beds from the latter is not very obvious. 
A fine series of strata belom^ino; to this division, 
occurs on the western side of Newhaven harbour, 
lying upon the chalk cliffs, which are there about 
fifty feet high. The summit of the hill is broken 
and rugged, and its appearance differs so remark- 
ably from the smooth rounded surface of the 
surrounding downs, that the geologist, even at 
a distance, would suspect the existence of strata 
very dissimilar to any that exist in the vicinity. 
Castle Hill is the Eastern extremity of the chalk 
cliffs, that extend from Rottingdean to Newhaven 
harbour, and is about a mile to the south of the 
town, on the west of the embouchure of the Ouse, 
eight miles from Lewes. Its summit bears marks 
