232 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. 



