1872.) Geology of the Straits of Dover. 213 
the lower part. The Weald Clay, as the highest division of 
these beds is called, can hardly be more than 500 feet thick 
on the Kentish coast,—probably it is less than that; but 
here there is no evidence by which we can determine its 
exact thickness. As a whole it is a stiff impervious clay, 
but it contains some thin beds of sand and limestone, which 
yield water. 
The more sandy division below is the Hastings Beds: 
here are thick beds of porous sand and sandstone, divided 
by the Wadhurst Clay, which closely resembles Weald Clay 
in character. The Ashburnham Beds form the base of the 
Hastings Beds. ‘These, as exposed on the coast, differ from 
the overlying Wealden division chiefly in the larger quanti- 
ties of coloured clay which they contain. As a whole, this 
division is impervious, but there are many bands of sand- 
stone which hold water. 
All the beds here described dip to the north-east, and suc- 
cessively disappear as we pass in that direction. A well 
sunk through any one of the strata described will certainly 
meet with that which has been described as underlying it ; 
but it is by no means certain that a well sunk, say, through 
the Chalk, would necessarily pass through the whole of those 
described. ‘The reason of this we will immediately see. 
Passing now to the French coast, we will suppose our- 
selves at Calais. This town stands on a wide flat of Tertiary 
beds covered up by sand and gravel. These beds underlie 
the whole of the flat country which stretches in a south- 
easterly direction past Guines. To the south of this there 
is rising and undulating ground, formed by the Chalk, which 
ends, as in Kent, with a fine escarpment. The various divi- 
sions of the Chalk are well seen along the cliffs between 
Sangatte and Wissant; these resemble those seen on the 
English coast, differing only in thickness, the Chalk-with-flints 
being much thinner on the French side of the Channel than 
on the English side. The lower divisions of the Chalk are 
more nearly alike. 
Cropping out from beneath the Chalk we find, at first, the 
same beds as on the English coast; there is a thin band of 
Upper Greensand, a thicker band of Gault clay, and below 
these the top sandy division of the Lower Greensand (Folke- 
stone Beds). These beds, as seen near Wissant, very 
closely resemble those of the English coast, differing only 
in thickness, they being each much thinner on the French 
than on the English coast. Perhaps the Folkestone Beds 
are the only division of the Lower Greensand which is here 
represented, for below them come some mottled clays, with 
