1872.] Geology of the Straits of Dover. air 
nent points of the range is a projecting spur crowned by a 
fine camp; it is known. as Cesar’s Camp, or Castle Hill. 
Looking northward from the crest of the escarpment, we 
see that the land falls away with an almost imperceptible 
slope. This plateau is furrowed by long valleys, which, 
commencing near the escarpment, run northward into the 
larger valley of the Dour, which enters the sea at Dover. 
Beyond the valley of the Dour the ground rises in a second 
escarpment, the high land of which again falls away north- 
ward into the low-lying lands of Deal and Minster. 
Returning now to the sea-cliff at Dover, and examining 
the rock of which it is composed, we shall find that, although 
all of chalk, it is of various kinds of chalk. The hill on 
which Dover Castle stands, and all to the north of it, is 
‘* Chalk-with-flints,” or ‘‘ Upper Chalk.”*. The hard flints, 
generally white outside but black when fractured, lying in 
regular rows, each row gradually inclining to the north, and 
thus showing the dip ot the beds. Passing again towards 
Folkestone, we find, soon after leaving Dover, that the chalk 
of the lower part of the cliff loses its flints, whilst they still 
continue on above, but get higher and higher above the sea- 
level, until at Folkestone Hill they only cap the cliff and 
escarpment. The lower division of the chalk is known as 
the “‘ Chalk-without-flints,” or ‘“‘ Lower Chalk.” Most of 
it resembles the Upper Chalk, save that flints are absent ; 
but the lower part of it is different in character. This 
is less pure in composition, contains some clayey matter, 
and is darker in colour than the overlying beds. This is the 
“*Grey chalk,” or “‘ Chalk marl,” the latter name being perhaps 
more properly employed for only the lowest part. The Grey 
Chalk rises from the shore a little east of Lydden Spout, and 
forms the base of the cliff, until we reach the undercliff, 
where it is in great part hidden by masses of fallen rock. 
It reappears at the base of Folkestone Hill, and can be 
traced from thence all along the lower slope of the escarp- 
ment. It is through this Grey Chalk that one proposed 
tunnel is intended to be driven. 
Emerging from beneath the Chalk, we find a thin band of 
green clayey sand (Upper Greensand). On the shore below 
the undercliff it is 20 feet or more in thickness, but inland 
it thins away, until, at the foot of Castle Hill, it is only 
18 inches thick; still further east it apparently disappears 
altogether for many miles. It is an important formation in 
* The chalk of the Isle of Thanet i is higher in the series than this. See a 
Paper by Mr. WuiTakeR, Quart. Journ. “Geol. Soc., vol. xxi., p. 3953; and 
Dowker, Geol. Mag., vol. vii., p. 466. 
