282 
EOCENE PERIOD. 
[Ch. XX, 
These newer strata of the Isle of Wight bear a certain de- 
gree of resemblance to some of the green marls and limestones 
in the Paris basin, yet, as a whole, no formations can be more 
dissimilar in mineral character than the Eocene deposits of 
England and Paris. In our own island the tertiary strata are 
more exclusively marine, and it might be said that the Parisian 
series differs chiefly from that of London in the very points in 
which it agrees with the formations of Auvergne, Cantal, and 
Velay. The tertiary formations of England are, in fact, almost 
exclusively of mechanical origin, and their composition be- 
speaks the absence of those mineral and thermal waters to 
which we have attributed the origin of the compact and sili- 
ceous limestones, the gypsum, and beds of pure flint, common 
to the Paris basin and Central France. 
English tertiary strata conformable to the chalk. — TheBritish 
Eocene strata are nearly conformable to the chalk on which 
they rest, being horizontal where the strata of the chalk are 
horizontal, and vertical where they are vertical. On the other 
hand, there are evident signs that the surface of the chalk had, 
in many places, been furrowed by the action of the waves and 
currents, before the Plastic clay and its sands were superim- 
posed. In the quarries near Rochester and Gravesend, for 
instance, fine examples are seen of deep indentations on the 
surface of the chalk, into which sand, together with rolled and 
angular pieces of chalk-flint, have been swept *. But these 
appearances may be referred to the action of water when the 
chalk began to emerge during the Eocene period, and they by 
no means warrant the conclusion, that the chalk had undergone 
any considerable change of position before the tertiary strata 
were superimposed. 
In this respect there is a marked difference between the 
reciprocal relations of our secondary and tertiary rocks and 
those which exist between the same groups throughout the 
greater part of the continent, especially in the neighbourhood 
of mountain-chains. Near the base, for example, of the Alps, 
* Con. and Phil., Outlines of Geol., p. 62. 
