and relations of the rocks and strata in which the most important fossils were discovered.

GEOLOGICAL STRUCTURE OF THE SOUTH-EAST OF ENGLAND. -The various strata that appear on the surface of the SouthEastern part of our island, constitute four natural groups or formations, namely, 1. The Drift, or Diluvium; 2. The Eocene, or Tertiary strata; 3. The Chalk formation; 4. The Wealden.

The Drift, or Diluvium.-These are the superficial accumulations which are irregularly spread over the surface, and form the immediate subsoil. They consist of layers of loam, clay, sand, gravel, and boulders, of variable extent and thickness, composed of waterworn materials which bear unequivocal evidence of having been drifted or transported from a distance by floods or inundations, or other agents of a like nature. Over considerable areas, as, for example, on both sides of the valley of the Thames, a fine silt or mud appears to have been deposited upon the drifted boulder-clay since the country had acquired its present physical configuration; and in this deposit, as well as in the ancient drift beneath, are found skeletons and detached bones and teeth of extinct species of Elephant, Rhinoceros, Hippopotamus, Elk, Ox, Horse, &c.; and, in some places, the remains of species still existing, are associated with those no longer known. Bones of carnivora, as the Hyæna, Bear, Tiger, Wolf, also occur in the drift, as well as in the ossiferous caves of which we shall treat when describing the contents of another department of the Museum.

The Tertiary or Eocene Strata of London.-The metropolis of England, like that of France, is built on the surface of a tertiary formation, consisting of beds of blue, yellow, and mottled clays, several hundred feet in thickness, with intercalations of loam, sand, gravel, &c. Some of the strata abound in extinct species and genera of marine shells, fishes, crustacea, &c.

The Chalk Formation.-The white calcareous rock of this formation is well known by the name of Chalk; but in the nomenclature of Geology, the term Chalk Formation comprises not only the pure limestone that extends over a considerable part of the country, but likewise subordinate strata of sand and sandstone, clays, marls, and limestones, very dissimilar in appearance and mineralogical character, but which present

such an accordance in the nature of the fossil remains imbedded in them, as to indicate that the entire series was accumulated while the same conditions of animal life prevailed. The organic remains of the chalk are essentially marine, and consist of many hundred species of shells, corals, radiariæ, &c. Numerous species and genera of fishes and crustaceans, and a few remains of reptiles, &c. obtained from the district under review, are deposited in the Gallery of the Museum. In some localities, drifted wood and fruits of terrestrial plants, and bones and teeth of reptiles, and other spoils of the land, have been discovered collocated with the usual marine productions, and these remains have evidently been carried down by rivers and streams into the sea, and transported by currents far from land, till they subsided in the depths of the ocean. One of the most remarkable instances of this kind is the portion of a skeleton of an Iguanodon discovered near Maidstone, in that division of the cretaceous greensand called the Kentish rag.

The Wealden.-An extensive series of clays, sands, and sandstones and shelly limestones, upwards of 1,000 feet in thickness, characterized by the terrestrial and fluviatile nature of the organic remains, and the almost entire absence of any relics of marine animals or plants.

ORDER OF SUPERPOSITION.-Such is the chronological sequence of the formations of the south-east of England; in other words, these several groups of marine and freshwater strata have been deposited in the following order, beginning with the lowermost or most ancient system :—

I. THE WEALDEN: the delta of a river, composed of the alluvial debris of an extensive continent. These strata are spread over the uppermost beds of the Oolite, a vast oceanic formation, but which does not come within the scope of our present observations.1

II. THE CHALK: the sediments of an ocean of great extent, deposited upon the Wealden.

III. THE TERTIARY OR EOCENE: accumulated in depressions on the surface of the Upper or White Chalk, consisting of marine, fluvio-marine, and lacustrine deposits.

With the view of simplifying the subject, the drift, or beds

1 See "Geology of the Isle of Wight,” p. 348.

P

of superficial transported materials, are omitted in the following commentary.

As each of these systems or formations is many hundred feet in thickness, it follows that the inferior strata would have been for ever concealed from observation, had the original order of superposition of the respective deposits remained undisturbed. But not only portions of each of the upper series, but even of the lowermost deposits, appear on the surface, and form an extensive tract of country, diversified by hills and valleys, and constituting one of the richest agricultural provinces of the British Isles. This distribution of the strata has originated from the displacements occasioned by those disturbing forces which have been in activity from the earliest periods of the present physical condition of the earth, and by which the beds of the ancient oceans and rivers have been elevated above the water, and converted into dry land. The nature of those changes we will now consider.

The Eocene deposits form the area on which London is situated, and extend over the surrounding country to a distance varying from ten to twenty or thirty miles. Around the margin of this series of strata the Chalk appears, and forms a distinct chain of hills on the south, west, and north; but on the east the range is broken by the valley through which the Thames winds its way to the sea. From this geological character of the metropolitan district, it results that all the lines of railway that proceed from London, traverse for the first ten or twenty miles beds of tertiary clay, loam, and loosely aggregated sand and gravel; hence the numerous slips that have taken place in the embankments at New Cross, Wandsworth, Hanwell, &c.; and in all these lines it is obvious from the nature of the soil and the steepness of the cuttings, that similar subsidences will again occur.

The next geological feature observable along the London railways is the Chalk, which is intersected by steep cuttings and tunnels; as for example in the South-eastern line, from Croydon to Merstham; and in the Great Western, from Maidenhead to beyond Wallingford. After passing through the Chalk, the lower subdivisions of the Cretaceous formation, viz. the Marl, Firestone, Galt, and Greensand, successively appear; and these are followed by the Oolite on the Great Western and Birmingham lines, and by the Wealden on the

South-eastern; but on the South-western the Chalk and the Tertiary strata only are exposed.

The Chalk, as is well known, constitutes the predominant geological feature of this part of England. The Upper or White Chalk rises into chains of hills called Downs, which are remarkable for their smooth and undulated outline, and form a well-defined geographical boundary. The southern range extends from Hampshire through Sussex to the sea-coast, terminating in the bold promontory of Beachy Head; the northern passes from Hampshire, through Surrey and Kent to the British Channel, and ends in the line of cliffs near Dover.

The lower Cretaceous strata compose ranges of hills less uniform in elevation and extent, which skirt the inner margin and escarpments of the Downs, and in some parts of Surrey and Western Sussex, attain an altitude equal to that of any portion of the North or South Downs. Leith Hill, in Surrey, is nearly 1,000 feet above the level of the sea.1

PHYSICAL GEOGRAPHY OF THE COUNTRY.-The Wealden deposits fill up the whole area between the North and South Downs, and are bounded on the west by the cretaceous strata of Hampshire, and on the east by the British Channel; they form the sea-coast from Pevensey in Sussex to Hythe in Kent.

Looking down upon the Wealden from any of the heights that command a view across the district, and of the distant boundary of chalk downs-as for example from Leith Hill, or from the summit of the escarpment of the North Downs, near Reigate—the observer might suppose that these freshwater sediments occupy a depression or basin on the surface of the chalk, and that the strata of the North and South Downs extend under the whole of the deposits in the intervening area.

GEOLOGY OF THE SOUTH-EAST OF ENGLAND. A slight examination of the natural sections of the respective strata where their relative position can be ascertained, is, however, sufficient to show the incorrectness of this hypothesis,

1 For details, vide a Memoir by the Author, "On the Geological Structure of the Country seen from Leith Hill," in the County History of Surrey; published by Mr. Ede of Dorking.

and to prove that the Wealden extends beneath the Chalk, both on the north and south, as shown in Lign. 47; and it is therefore certain that the Cretaceous strata were deposited upon the Wealden, and that they originally extended over the entire district between the North and South Downs, and were connected on the west with those of Hampshire and Wiltshire, and also occupied the area now covered by the British Channel; the chalk of the Isle of Wight being then continuous with the corresponding strata of the opposite coast of the Continent.

A careful examination of the phenomena under review, demonstrates that the removal of the chalk was not effected simply by denudation, but by a force acting from beneath, which broke up and elevated masses of the Tertiary, Cretaceous, and Wealden formations, in a line bearing a general direction from east to west; by this movement an anticlinal' position was given to the strata on each side the axis of greatest elevation. This axis is shown in the physical geography of the district by the chain of hills called the Forest-Range, that extends from the sea-coast at Hastings through the interior of the country by Crowborough Hillan elevation of nearly 600 feet-to Loxwood, west of Horsham, where the Wealden disappears beneath the overlying greensand strata.

SECTION FROM LONDON TO THE SOUTH-COAST.-In all transverse sections of the district, i. e. from north to south, the strata on the north of the central line dip to the north-east, and those on the south to the south-west. There are, of course, many local variations in the inclination of the rocks, and numerous lesser anticlinal axes, or saddles, as they are provincially termed, and also longitudinal ridges and corresponding valleys, running parallel with the principal line of the disturbing force.

In consequence of this displacement of the strata, a seotion drawn from London through the North Downs, across the Wealden district, and through the South Downs, and carried on to the southern coast of the Isle of Wight, would present the arrangement shown in Lign. 46; in which are

1 Anticlinal-a geological term, signifying inclined towards each other, like the ridge-tiles of the roof of a house.