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Ir is now more than three years since the appearance of the last Edition of the Manual (published January, 1851). In that interval the science of Geology has been advancing as usual at a rapid pace, making it desirable to notice many new facts and opinions, and to consider their bearing on the previously acquired stock of knowledge. In my attempt to bring up the information contained in this Treatise to the present state of the science, I have added no less than 200 new Illustrations and 140 new pages of Text, which, if printed separately and in a less condensed form, might have constituted alone a volume of respectable size. To give in detail a list of all the minor corrections and changes would be tedious; but I have thought it useful, in order to enable the reader of former editions to direct his attention at once to what is new, to offer the following summary of the more important additions and alterations.

Principal Additions and Alterations in the present Edition.

CHAP. IX. "The general Table of Fossiliferous strata," formerly placed at the end of Chapter XXVII., is now given at p. 104, that the beginner may accustom himself from the first to refer to it from time to time when studying the numerous subdivisions into which it is now necessary to separate the chronological series of rocks. The Table has been enlarged by a column of Foreign Equivalents, comprising the names and localities of some of the best known strata in other countries of contemporaneous date with British Formations.

CHAP. XIV. XVI.-The classification of the Tertiary formations has been adapted to the information gained by me during a tour made in the summer of 1851 in France and Belgium. The results of my survey were printed in the Quarterly Journal of the Geological Society of London for

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, I 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 Bagshot 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 organic remains, not given in previous editions.

CHAP. XVII.-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. XVIII.-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 problem by an appeal to ordinary causation, or to invoke the aid of imaginary catastrophes and paroxysmal violence, pp. 271-290.

CHAP. XX.-XXI.-On the strata from the Oolite to the Lias inclusive. The Purbeck beds are here for the first time considered as the uppermost member of the Oolite, in accordance with the opinions of the

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