54 
CASTLE HILL. 
of an ancient entrenchment, which, when first 
constructed, must have embraced an area of twelve 
or fourteen acres ; although, from tlie encroach- 
ments of the ocean, scarcely a third of it remains. 
The hill is about 180 feet high, and presents a 
ruinous aspect towards tiie sea : near the edge of 
the cliff’, the strata are in so crumbling a state, and 
the fissures so numerous, as to render their examin- 
ation difficult and dangerous. From the decom- 
position and destruction of the strata which are 
constantly going on, their surface seldom exposes 
an instructive section, except after recent falls of 
the cliff. The thickness of the strata, exclusivelv of 
the chalk, does not exceed seventy or eighty feet ; 
and they reach along tlie coast to about a mile 
west of the signal house, gradually becoming less, 
till a thin cap of clay and sand marks their termin- 
ation. 
Commencing with tlie uppermost bed, the cliff’ 
is composed of, 
1. Sand and pebbles, — from 10 to 15 feet. 
Coarse argillaceous rock ; chiefly composed 
of oyster shells ; with a few cerithia, &c., — 5 feet. 
3. Foliated blue clay, with an immense quantity 
of shells ; the upper part contains shells of the ge- 
nera Cytherea and Cyclas ; the lower division Ce- 
rithia, and teeth of sharks *, — 10 feet. 
4. Reddish brown marl, more or less slaty, bear- 
ing impressions of leaves, wood, cones of a plant 
of the palm tribe ? and casts of Potamides and 
Cyclades, — from 4 to 5 inches. 
* A few shells of the genus Cyrcna have been discovered in it. 
