VI PREFACE TO THE FIFTH EDITION. 



1852. In the course of my investigations I enjoyed opportunities of 

 determining more exactly the relations of the Antwerp and the Suffolk 

 crag, p. 173 ; the stratigraphical place of the Bolderberg beds near 

 Hasselt, p. 178 ; that of the Limburg or Kleyn Spawen strata, p. 188 ; 

 and of other Belgian and French deposits. In reference to some of these, 

 the questions so much controverted of late, whether certain groups should 

 be called Lower Miocene or Upper Eocene, are fully discussed, p. 183, 

 et seq. 



In the winter of 1852, 1 had the advantage of examining the northern 

 part of the Isle of Wight, in company with my friend the late lamented 

 Professor Edward Forbes, who pointed out to me the discoveries he had 

 just made in regard to the true position of the Hempstead series 

 (pp. 185-192), recognized by him as the equivalent of the Kleyn 

 Spawen or Limburg beds, and his new views in regard to the relation of 

 various members of the Eocene series between the Hempstead and Bag- 

 shot beds. An account of these discoveries, with the names of the new 

 subdivisions, is given at pp. 208 et seq. ; the whole having been revised 

 when in print by Edward Forbes. 



The position assigned by Mr. Prestwich to the Thanet sands, as an 

 Eocene formation inferior to the Woolwich beds, is treated of at p. 221, 

 and the relations of the Middle and Lower Eocene of France to various 

 deposits in the Isle of Wight and Hampshire at p. 222 et seq. In the 

 same chapters, many figures have been introduced of characteristic or- 

 ganic remains, not given in previous editions. 



Chap. XVH. — In speaking of the Cretaceous strata, I have for the first 

 time alluded to the position of the Pisolitic Limestone in France, and 

 other formations in Belgium intermediate between the White Chalk and 

 Thanet beds, p. 235. 



Chap. XVIH. — The Wealden beds, comprising the Weald Clay and 

 Hastings Sands apart from the Purbeck, are in this chapter for the first 

 time considered as belonging to the Lower Cretaceous Group, and the 

 reasons for the change are stated at p. 263. 



Chap. XIX. — Relates to " the denudation of the Weald," or of the 

 country intervening between the North and South Downs. It has been 

 almost entirely rewritten, and some new illustrations introduced. Many 

 geologists have gone over that region again and again of late years, 

 bringing to light new facts, and speculating on the probable time, extent, 

 and causes of so vast a removal of rock. I have endeavored to show how 

 numerous have been the periods of denudation, how vast the duration of 

 some of them, and how little the necessity to despair of solving the prob- 

 lem by an appeal to ordinary causation, or to invoke the aid of imagi- 

 nary catastrophes and paroxysmal violence, pp. 271-290. 



Chap. XX. — XXI. — On the strata from the Oolite to the Lias inclu- 

 sive. The Purbeck beds are here for the first time considered as the 

 uppermost member of the Oolite, in accordance with the opinions of the 



