214 Geology of the Straits of Dover. (April, 
sand, ironstone, and pebbles, which represent the thick 
Wealden formation of the English coast. The thickness of 
these is uncertain, but probably it nowhere exceeds 100 feet. 
Below them come the Oolitic rocks, which are not exposed 
on the coast of Kent or Sussex. We need not minutely 
describe these rocks. Only the higher divisions (Portland 
and Kimeridge Beds) are seen along the coast, the lower 
divisions cropping out inland. On the north-east of Mar- 
quise there are still lower beds, of the Carboniferous, De- 
vonian, and Silurian formations, which occupy only a few 
square miles of the surface, but are known to underlie the 
higher rocks, at no great depth, over a great extent of 
country. 
The Chalk escarpment which is cut by the coast near 
Wissant passes in a curved line round the country, and 
meets the coast again near Neufchatel, on the south of 
Boulogne. In a similar manner, the Chalk escarpment 
which is cut by the English coast at Folkestone passes 
round the country to the west, and reaches the Channel 
again at Beachy Head. ‘The large district thus enclosed 
by the Chalk escarpment, on the English side, is known as 
the Weald. ‘The similar district enclosed by the Chalk es- 
carpment on the French side of the Channel is known as the 
Bas-Boulonnais. Although these two districts are now 
separated by the English Channel and the Straits of Dover, 
geologically considered they are one and the same. 
Such being the geological structure of the coasts, we have 
now to consider what is the probable structure of the bed of 
the Channel. Here, of course, we can only be guided by 
analogy. We are entitled to assume that beds which have 
a constant character wherever we can study them, will pro- 
bably maintain that character throughout the short space 
which intervenes between the French and English coasts. 
The beds of Chalk, which resemble each other on both sides, 
will, without doubt, have the same charaé¢ter beneath the 
bed of the Channel. When the beds are thicker on the one 
side than on the other, as is the case with the Chalk-with- 
flints, the intervening area will be occupied by that forma- 
tion having its proper general character, but gradually 
diminishing in thickness as we pass from England to France. 
So, again, with the Gault ; as there is no place all round the 
Weald and the Bas-Boulonnais where this division is ab- 
sent, we may be perfectly sure that it is present in its proper 
position in the bed of the Channel, but with diminishing 
thickness as we pass from England to France. So, also, 
with the Folkestone Beds, which in the south-east of 
