CHAPTER XIV.


CRETACEOUS SERIES.

WHEN the continent described in last chapter had endured for a long period of time, submergence of the area began to take place, accompanied by the deposition of the purely marine CRETACEOUS SERIES, which in England is as follows, the oldest beds being placed at
the bottom:


I may here mention that in parts of the Continent of Europe, there are certain marine formations intermediate in position and date between the Oolitic and Cretaceous rocks, which are known as the Neocomian beds, so called from Neocomium, the ancient name of Neuchâtel, in Switzerland, where they are well developed. The assumption that the Hastings Sands and Weald Clay are the fresh-water equivalents in time of the lower and middle parts of these continental beds, is undoubtedly correct, the Lower Greensand of English geologists being the British representative of the Upper Neocomian strata.

Mr. Judd has shown that at the south end of Filey

[Atherfield Clay. 213]

Bay, in Yorkshire, we have the actual marine representatives of the continental Neocomian strata. These Yorkshire beds were formerly called Speeton Clay, and lie between the uppermost Oolitic strata of the district, called by Mr. Judd, Portlandian, and the Red Chalk or Hunstanton Limestone, which, according to that author, cannot be of later age than the Upper Greensand, and may he as early as the Gault.1

The area occupied by the Purbeck and Wealden strata underwent a long period of slow depression, during which these fresh-water strata with occasional marine interstratifications were deposited; and by sinking still further, the purely marine beds of the Atherfield Clay began to be formed. In fact, but for the presence in it of marine fossils, it is hard to draw any line between the Wealden and the Atherfield Clays, and no doubt the mud that formed the latter was at first carried seaward by the same great river, in the manner, for example, that muddy sediments are now deposited at and near the mouth of the Amazons on the east coast of South America.

The Atherfield Clay takes its name from Atherfield, on the south-west coast of the Isle of Wight, where it is well seen overlying the Weald Clay, and is overlaid by the Lower Greensand.  Its lowest beds form a kind of passage from the fresh-water strata of the Weald into the overlying marine beds of the Lower Greensand, both in the Isle of Wight and in the Wealden district, round which it circles at the edge of the Lower Greensand; for at Atherfield there seems to have been a depression of the fresh-water area and an influx of the sea, accompanied by the appearance of Cerithium carbonarium, accompanied by Pinna and Panopœa standing vertically in the position in which they lived. Many other shells

1 'Journal of the Geological Society,' 1868, vol. xxiv., p. 218.

[214 Lower Greensand.]

are scattered through the clay, including the well-known Perna Mulleti, Trigonia caudata, Gervillia aviculoides, Areas, Pectens, Oysters, Rostellaria Parkinsoni, and Hemicardium Austeni, &c. &c.

THE LOWER GREENSAND, of which the Atherfield Clay is a subdivision, comes next in succession, in the Isle of Wight, beginning with a bed of sandstone containing Gryphœa sinuata and many other shells, succeeded by 29 feet of clay, vulgarly called the 'lobster bed,' from the presence of Meyeria magna, formerly called Astacus, together with Ammonites Deshayesii, &c., overlaid by nodular bands with Gervillia aviculoides, &c.., above which, clay is repeated, with the same Meyeria. Above this, sands and clays alternate to the top of the series, with many fossils, among which may be mentioned as characteristic, Terebratula sella, T. Gibbsii, T. biplicata, Limas, Gryphœ
as, Gervillia solenoides, Ammonites, Nautili, and other remarkable Cephalopoda of the genera Crioceras, Ancyloceras, and Hamites. The whole of these strata overlying the Wealden beds occur in magnificent sections along the southern cliffs of the Isle of Wight, dipping northerly under the Gault, Upper Greensand, and Chalk, which in a high ridge stretches across the island from Culver Cliff to Alum Bay. Overlaid by the Gault, and reposing on the Weald Clay, the Lower Greensand also sweeps round the whole Wealden area from Sandgate to Guildford and Haslemere, and from thence to the coast north of Beachy Head. Between Guildford and Haslemere it forms high scarped terraces. The sands are sometimes quite soft, with intercalated hard bands, and they are frequently ferruginous. A good building stone, very fossiliferous, being sometimes an impure limestone, called the Kentish rag, lies in the lower part
FIG. 42.

Atherfield Clay and Lower Greensand Fossils

Group of Atherfield Clay and Lower Greensand Fossils.


[216 Lower Greensand.]

of the formation, on the north side of the Weald at Maidstone. It rests on the Atherfield Clay. The general grouping of the fossils in all this area correspon is with that of the Isle of Wight. In Dorsetshire and part of Somersetshire, at the south end of the western escarpments of the Cretaceous rocks, the Lower Greensand is absent, and the Upper Greensand rests directly on the Lias and New Bed series. Further north, the Lower Green sand reappears in Wiltshire, near Chapmanslade, about three miles east of Frome, and in a long narrow band follows the direction of the escarpment of Chalk, as far as the neighbourhood of Devizes, where it widens for a space, and runs north in a projecting tongue as far as Farringdon, where it is known as the Sponge gravel.

Beyond the Farringdon area, it is for a space of twelve miles overlapped unconformably by the Gault, to reappear a little south of Abingdon in a broad patch, that extends eastward about six miles to Chiselhampton, where it is again overlapped by the Gault, to reappear in a narrow strip between Great Hazeley and the neighbourhood of Thame. Several small outliers of Lower Greensand lie on the Purbeck strata, south, west, and north of Aylesbury. At Leighton Buzzard it appears in great force, covering all the country for miles round Woburn, from whence it trends away to the north-east, and disappears under the alluvium of the Fens of Cambridgeshire, and runs along the east side of the Wash, where, crossing under sea, it reappears in Lincolnshire, and following the line of the chalk escarpment runs in a NNW. line to the Humber. As a whole this formation may be described as consisting of yellow, grey, white, and green sands.

In the Weald country and on the north-west

[Lower Greensand. 217]

side of the great Chalk escarpment, between Devizes and the Wash, the Lower Greensand is often ferruginous, and has been worked for iron ore both in ancient and modern times. Fossil wood is of frequent occurrence, perhaps of Coniferous trees, and all the evidence tends to show that, in the English area, the strata were deposited in comparatively shallow seas not far from shore.

The general characters of the fossils of the series are as follows:—Echinoderms of the genera Salenia, Cardiaster, Diadema, Discoidea, Echinobrissus, together with Pentacrinites, are found in it. Terebratulœ and Rhynchonellœ are of frequent occurrence, with a few other Brachiopoda. Among the Lamellibranchiate molluscs are numerous Limas, Gervillias, Perna, Oysters, Pectens, and Pinnas, together with shells of the genera Cardium, Venus, Trigonia, Myacites, and Nucula. Gasteropoda are not generally numerous. Cephalopoda of remarkable forms are characteristic; for, in addition to several species of Ammonites, Nautili, and Belemnites, there are Crioceras, and Ancyloceras, like Ammonites half unrolled, Crioceras Bowerbankii, Ancyloceras gigas, A. grande, and A. Hillsii. Fishes are scarce, and only three reptiles have hitherto been described, one Chelonian, Protemys serrata, a Plesiosaurus, and a crocodilian saurian Polyptychodon continuus, said also to occur in the Lower Chalk.

Out of about 300 Lower Greensand species, 18 or 20 per cent. pass into the Upper Cretaceous series. Partly for palæontological considerations, and also because the Gault seems sometimes to lie, as it were, unconformably on the eroded surface of the sand, the dissimilarity in the grouping of fossils is so great, that

[218 Gault.]

it has been considered advisable to draw a marked line between the two groups; the Atherfield Clay and the Lower Greensand, when the term Neocomian is not applied to them, meaning Lower Cretaceous, and all above them to the topmost beds of the Chalk being considered as Upper Cretaceous strata.

The GAULT forms the base of the Upper Cretaceous series—or of the Cretaceous series, for those who choose to call the Lower Greensand Neocomian. It is a stiff blue clay, about 300 feet thick in its thickest development, but sometimes it is hard to separate it lithologically from the Upper Greensand. It appears in the Isle of Wight, overlying the Lower Greensand all across the Island; and ranges round the escarpment of the Weald in the same position, with occasional signs of a kind of unconformable erosion between them; and in the centre of England, from the neighbourhood of Devizes to the Wash in Norfolk, the Gault occasionally completely overlaps the Lower Green sand in an unconformable manner. In proof of this unconformity, occasional outlying patches of the Lower Greensand occur north of the Chalk escarpment, without any visible signs of it immediately at the base of the neighbouring Upper Cretaceous strata, which there ought to be, if these formations lay everywhere conformably on the Lower Greensand.

Many Foraminifera have been found in the Gault, and a few Corals, Cyclocyathus Fittoni, Trochosmilia sulcata, and Caryophyllia Bowerbankii. Its sea-urchins are of the genera Cidarius (C. Gaultina), Hemiaster (H. Asterias, H. Baileyi), and Diadema tumida. It contains many Crustaceans, such as Astacus, Etyus Martini, Diaulax Carteriana, Palœocorystes Stokesii, &c. Among the Brachiopoda and Lamellibranchiate

[Gault. 219]

molluscs the following are characteristic :—Terebratula biplicata, Rhynchonella sulcata, Oysters, Pectens, Plicatula pectinoides, Pinna tetragona, &c. ; Gervillia solenoides, Inoceramus sulcatus, &c.; Lima parallela, Cucullœa, Arca, Nucula pectinata, &c. it also yields Gasteropoda of the genera Dentalium, Solarium, Scalaria, Natica Gaultina, Pleurotomnaria Gibbsii, Rostellaria carinata, &c., and many Cephalopoda, such

FIG. 43.
Gault Fossils

Group of Gault Fossils.


as Belemnites minimus, &C. ; Nautilus inequalis, &c. ; Ammonites splendens, A. dentatus, A. interruptus, A. lautus, &c. &c. ; Ancyloceras spinigerum, Hamites attenuatus; H. rotundus, &.c. Traces of the Gault may probably be found along the lower outskirts of the Chalk all the way to Filey Bay in Yorkshire, where the Red Chalk has by some been considered to be its equivalent, or, at all events, to be of a

[220 Upper Greensand.]

geological date, not later than its successor the Upper Greensand.

It would be a great comfort to a proportion of the geological population, if the different formations were as clearly distinguishable on the ground, as they are on a map, by different colours, aided by numbers or letters for the use of the colour-blind. If to this, in the economy of Nature, it had so happened that no species had been permitted to stray from its own formation into the next in succession, the benefit would have been much enhanced, for to those with keen eyes for form, the finding of any single fossil would be sufficient to mark the place in the geological scale of any given formation. Then we should have a perfect and orderly symmetrical accuracy of detail, so that he who runs may read. But it so happens that this is not the case, for Nature loves variety, and performs her functions in various ways, and thus it happens that in certain cases the dividing lines between two formations, if we follow them far enough, are sometimes difficult to determine. Of these unruly formations in England the Upper Greensand forms one, in its occasional physical relations to its neighbours, the Gault below and the Chalk above.

THE UPPER GREENSAND in the West of England appears in great force, forming part of the strata that extend from the coast between Lyme Regis and Sidmouth, northward to the Black Down Hills, south of Taunton. West of the estuary of the Exe, it forms, in two outlying patches, the broad-topped hills of Great Hal-don and Little Hal-don, and south of the angle of the Teign, near Newton Bushell, there is another outlier on Milber Down. These lie so near the main mass, and approximately are so much on the same level, that they

[Upper Greensand. 221]


are obviously the work of ordinary denuding agencies on a broader area of Greensand. It is, however, at first sight somewhat surprising, to meet with a small outlier of Upper Greensand, only a few acres in extent, nearly fifty miles to the west of Black Down, at Orleigh Court, three miles south-east of Bideford Bay. This patch is mentioned by De la Beche, in his Report on the Geology of Cornwall, Devon, and West Somerset, and of late its existence as a solid outlier has been doubted. There is, however, so much angular chert on the spot, that sufficient material remains to show that the Greensand once spread westward so far, and in my opinion probably much farther,

Throughout these areas, the Upper Greensand may be briefly described as consisting of yellowish brown sand, partly compact, partly soft, with layers and detached pieces of chert, and towards the base it is partly green with specks of silicate of iron. The sands are often coarse, and contain layers of shells, frequently broken and fragmentary. The whole is little more than 200 feet in thickness.

East of Lyme Regis, this Greensand appears near Abbotsbury, on the southern and western flanks of the Chalk Downs at Whitehill. West of Chideock outlying patches lie on the maristone of the Middle Lias, between Chideock and Bridport on the sand that underlies the Inferior Oolite, at Abbotsbury Castle on the Forest Marble, and from thence stretching north and west, at Shipton Beacon they lie on the Fuller's Earth. Beyond this the Cretaceous strata make a great. curve east of Poorstock and Beaminster, lying generally on the Fuller's Earth. East of Cheddingtori, for some miles the Greensand lies on the Oxford Clay, then for a short space on the sand of the Calcareous

[222 Upper Greensand.]

Grit, then from Buckland Newton, in Dorsetshire, to the neighbourhood of Shaftesbury, on Kimeridge Clay.

Near Shaftesbury the Gault comes on in force, and separates the Upper Greensand from the Oolitic rocks as far as the neighbourhood of East Knoyle, on the north side of the mouth of the Vale of Wardour. Between East Knoyle and Chapmanslade in Wiltshire, the Greensand lies chiefly on the Coral Rag, but partly on the underlying Oxford Clay, and the Gault, if present at all, is so thin that it cannot be mapped. It is probable that when the Gault was deposited elsewhere, this part of the Oolitic area was above the sea-level. From Chapmanslade, the Greensand, underlaid by Gault, runs along the lower part of the Chalk escarpment in an ENE. direction, by Westbury to Urchfont and Devizes, and from thence, lying nearly flat, the strata form the surface of a broad tract of country, eighteen miles in length from west to east, bounded on both sides by Chalk, the whole forming a low anticlinal north and south curve. Still further east, at Shalbourne and Sidmonton, near .Kingsclere in Hampshire, two other tracts of Upper Greensand rise through the Chalk to the surface in anticlinal curves of an oval form.

Between Devizes, the Fens of Cambridgeshire, and the east coast of the Wash, the Upper Greensand runs to the north-east, in a long somewhat sinuous line, and nearly all along the strike it forms the lower part of the bold escarpment of the Chalk, which overlooks the great plain or table-land of Oolitic strata that runs across England from the coast of Dorsetshire to the Humber. North of the Humber, it is marked in ordinary maps as skirting the Chalk Wolds, first to the north and then to the east, as far as Filey Bay, but if such be the case, its sandy character is not always

[Upper Greensand. 223]

easily recognisable, which, indeed, is also the case much further south.

In the south-eastern part of Dorsetshire, the Upper Greensand crosses the Isle of Purbeck from west to east in a narrow line, overlying the well-known Punfield beds, and overlaid by the Chalk of the long and imposing ridge of Purbeck Hill, Knowl Hill, Nine Barrow Down, and Ballard Down. The Greensand itself makes no feature in the landscape. Fig. 75, p. 347.

Striking east under the sea, the Upper Greensand barely escapes forming part cf the great seacliff of chalk, that runs from Sun Corner near the Needles, to Compton Bay below Afton Down, from whence, overlying the Gault, it crosses the Island to the sea close under Bembridge Down. In this course, wherever the Chalk Downs are narrow, owing to the high angle of northern dip, there the line of Upper Greensand is also narrow, but where the angle of inclination is comparatively low, there both Chalk and Greensand spread over a broad space, between Mollestone Down and Carisbrook. A large outlier of Upper Greensand, capped by two outliers of Chalk, overlooks the sea on the south side of the Island between Chale Bay and Chine Head, the strata being nearly flat.

In the area of the Weald of Kent and Sussex (fig. 72), the Upper Greensand at the base of the escarpment of the Chalk, sweeps round the vast oval, from East Wear Bay, near Folkestone, to East Meon, near Petersfield, and from thence to the sea at Eastbourne, near Beechy Head, but not with absolute certainty all the way, for only here and there can the Greensand be faintly discovered, between the sea and Chevening, along a line of about fifty miles in length. Beyond this point it begins to get more distinct, and the malm-rock, fire-stone,

[224 Upper Greensand.]

and other lithological varieties, can be traced all along by Westerham, Merstham, Guildford, the Hog's Back, Farnham, and the extreme west of the area in the country round Binstead, Selbourne, and the ground about two miles west and south of Petersfield, where, as far as colour goes, it might often be taken for chalk.

On the south side of the Wealden area, the Upper Greensand maintains the same general character by Cocking and Barlavington as far as Steyning, where its lithological character begins to change, and the beds pass into 'sandy marl and marly sand,' and near Eastbourne the strata are decidedly sandy.

Important deductions are to be drawn from the consideration of the lithological changes that take place in the character of the Upper Greensand, which will afterwards appear. A gradual change may be traced all the way from Devonshire to Cambridgeshire and the east end of the Wealden area, which throws some light on the physical geography of the time, especially when taken in connection with the circumstance, that out of more than 200 species of fossils in the Gault, about 46 per cent. pass onward into the Upper Greensand.1 The Upper Greensand is often fossiliferous, containing Cycads and Coniferous woods; Sponges, Siphonia, pyriformis, &c.; a few Foraminifera; Corals, Trochosmilia tuberosa, Micrabacia coronula; many Echinoidea, the chief of which belong to the genera Cidaris, Cardiaster, Echinus, Pseudo-diadema, Salenia, &c. Brachiopoda are common, Terebratulœ and Rhynchonellœ (T. biplicata, Rh. latissima,

1 For much information on the Upper Greensand of the Wealden area see 'Memoirs of the Geological Survey, Geology of the Weald,' by W. Topley, 1875.

[Upper Greensand. 225]

&c.). In Lamellibranchiate molluscs it is even richer than the Lower Greensand, abounding especially in species of the genera Inoceramus, Gryphœa (1avigata), Lima, Pecten asper, Astarte, Trigonia, Cucullœa, Cyprina, and Cytherea. It is also rich in Gasteropoda, such as Turritella, Pleurotomaria, Natica (Y. Gentii), &c., and yields many species of Ammonites, Nautili,

FIG. 44.

Upper Greensand Fossils

Group of Upper Greensand Fossils.


Hamites, Baculites, Scaphites, and Belemnites. Crustacea, Hoploparia longimana, Necrocarcinus Bechii, &c. Probably three species of Reptilia belong to this formation, Plesiosaurus pachycomus, a Crocodile, and a Turtle.

THE CHALK, from its familiar characters and general uniformity of structure, is the most easily recognisable

[226 Chloritic and Chalk Marl.]

of all the British formations. From west to east it stretches from the neighbourhood of Beaminster in Dorsetshire, to Beachy Head and the North Foreland, and passing beneath the Eocene formations of the Hampshire and London basins it spreads northward to Speeton, in Yorkshire.

The Chloritic Marl indicates a passage from the Upper Greensand into the Chalk. It consists of a chalky base specked with green grains, and varies from a few inches to a few feet in thickness. It is highly fossififerous, abounding in Ammonites, Nautili (N. lœvigata), and a small Scaphite (S. œqualis), besides Oysters, Trigonias, Holaster, &c., and many other Echinodermata.

The Chalk Marl, which lies above the Chloritic Marl when both are present, is merely chalk with a slight admixture of argillaceous matter, and with its predecessor by no means deserves to be considered as a separate formation. The whole, therefore, may be massed as The Chalk. It consists of a soft white limestone, generally much jointed where exposed in quarries, and but for lines of flints, the bedding would often be scarcely distinguishable. On minute examination with the microscope, much of the Chalk is found to consist of the shells of Foraminifera, Diatomaceæ, spiculæ and other remains of Sponges, Polyzoa, and shells, highly comminuted. Somewhat similar deposits are now forming in the open Atlantic at great depths, chiefly of Foraminifera of the genus Globigerina, Polycystina and Diatomaceæ, and spiculæ of Sponges. In the Pacific, also, from Java to the Low Archipelago, over an area of about 4,000 miles in length, all the deep-sea deposits are of fine, white, calcareous mud, like unconsolidated chalk. In its thickest development in England the Chalk is

[The Chalk. 227]

about 1,200 feet thick in Dorsetsliire, Hampshire, &c. The Lower Chalk usually contains no flints and,as already stated, is somewhat many at the base, while the Upper Chalk is interstratified with many beds of interrupted flints. These are of irregular form, and lie in layers in the lines of bedding. A great proportion of them are stated by Dr. Bowerbank to be silicified Sponges, which often inclose other organic bodies, such as shells, fragments of Belemnites, &c.; others of large size, called Paramoudras, which are rare, stand vertically across the beds. These sometimes resemble, in general form, the large cup-shaped sponges of the Indian Ocean Alcyonium, or Neptune's cup.

As a whole, the Chalk dips gently from its western escarpment to the east and south, and round the Wealden area to the south and north, underlying the Tertiary strata of the Hampshire and London basins, and reappearing with precisely the same characters on the coast of France. Its area in Europe and Asia is immense. In the north of Ireland, between Belfast and the Giant's Causeway, there are patches of very hard Chalk on the coast, overlaid by columnar basalt of Miocene age. The great superincumbent pressure of these masses of igneous rocks has hardened the chalk, and therefore they have not, as is usually supposed, been altered by the heat of overflowing lavas, except possibly for an inch or two at the immediate point of junction, but this is somewhat foreign to our present subject. Traces of Chalk and Upper Greensand occur at Bogingarry, &c., in Aberdeenshire. These consist partly of chalk flints, partly of sandstone, possibly in place, and sufficient to show that Cretaceous rocks, which have been removed by denudation, probably once spread over that country. Cretaceous strata, discovered by Mr.

[228 The Chalk]

Judd, also occur in the Island of Mull beneath the Miocene basalts.

About half the genera, and a considerable number of Chalk species, are identical with those of the Gault and Upper Greensand, but it contains a far greater number, nearly 800, most of which are peculiar to itself. Plants are few, as might he expected in a wide deep-sea deposit. A great many Sponges have been described, chiefly from flints. Among the most numerous are species belonging to the genera Ventriculites, Gephalites, Spongia, and Siphonia. A large number of genera and species of Foraminifera are also described, among which Globigerina bulloides, Dentalina gracilis, and Rotalina ornata, are common. Of Corals about 15 species are known, several of which belong to the genus Parasmilia (centralis, &c.), Caryophillia lœvigata, &c. Echinodermata are very numerous, among others including the genera Ananchytes, Cardiaster, Cidaris, Cyphosoma, Diadema, Echinopsis, Galerites and Echinobrissus, Holaster, Micraster, and Solenia, &c. Among its starfish are comprised the genera Arthraster, Goniaster, and Oreaster. Of these Goniaster is exceedingly characteristic. In addition it has yielded an Ophiura and several Crinoids, Bourgueticrinus ellipticus, Marsupites Milleri, &c. On shells, &c., found in the Chalk, are frequent Serpulæ. It also yields Cirripeds and a few Crustaceans, Enoploclytia Sussexensis &c. Polyzoa are numerous, of many species. Like other members of the Cretaceous rocks, its Brachiopoda generically resemble those of the Oolites, including Rhynconella, Terebratulina, and Terebratula. The Lamellibranchiate molluscs of the Chalk are in some cases specifically identical with those of the Gault and Upper Greensand; and, generically, they bear the

[229]

FIG. 45.

Chalk Fossils

Group of Fossils from the Chalk.


[230 The chalk.]

strongest resemblance, consisting, among others, of many species of Inoceramus, Lima, Pecten, Oyster, Spondylus, Radiolites, Trigonia, &c. Being a deepsea deposit, it is poor in Gasteropoda, but rich in Cephalopoda, especially in Nautili (N. elegans, &c), Ammonites (A. Rothomagensis, &c.), and Turrilites (T. costatus), besides Baculites, Hamites simplex, Scaphites (S. œqualis), and Belemnites.

Numerically as individually, though still very characteristic, Cephalopoda are less numerous in the Cretaceous than in the Oolitic and Liassic strata, though the latter contain fewer genera. In the Lias and Oolites there are nearly 300 species of Cephalopoda, most of which are Ammonites. In the Cretaceous rocks less than 200 species are known, about 70 of which are Ammonites. More than 80 species of fish are known in the Chalk, including all the four orders of Agassiz, Placoids, Ganoids, Cycloids, and Ctenoids. Many of the Placoids are Cestraciont fish, numerous species being of the genus Ptychodus. Ten genera of reptiles are known, two of which are allied to the Crocodilia, Acanthophilis horridus, and Leiodon anceps ; the great Mosasaurus, 3 species; Plesiosaurus, 2 species, Ichthyosaurus and Pterodactyle, one of which is said to have measured eighteen feet across the expanded wings. Several Turtles occur in the Chalk, Chelone Bertstedi, &c.

Having thus briefly described the Tipper Cretaceous strata of England, I shall next endeavour to show what inferences may be drawn with regard to the physical geography of the British area, during the time occupied by their deposition.

We have already seen that, during the deposition of the Purbeck and Wealden strata, England formed part

[Physical Geography. 231]

of a great continent, and that, during the formation of the Lower Greensand, this land suffered partial submergence, but by no means to such an extent that the Oolitic strata, which then extended far to the west, round Wales, were entirely sunk beneath the sea in which our Lower Greensand was deposited.

As a whole, the Lower Greensand, being a coarse and sandy formation, was deposited in shallow water, and great part of it was in the long run tranquilly heaved out of the sea, to undergo terrestrial waste and denudation before the deposition of the Gault began.

The deposition of the Gault in our area, first took place on a surface of country that was being gradually submerged, and part of the sediment was laid on the Lower Greensand, and part on various members of the Oolitic strata, from which the Lower Greensand had been removed by denudation. This Gault Clay is, however, so difficult to separate from the Upper Greensand in the eastern part of England, and the Upper Greensand is so difficult to separate by any clear line from the Chalk, that it now becomes necessary to consider the question of the mode of deposition of all three, if, indeed, except as local developments of different sedimentary character, they ought not to be considered, on a broad scale, as only one formation. Right or wrong, the origin of this idea was first declared by Mr. Godwin-Austen, whose large grasp of questions in physical geology, (to be found only in scattered memoirs, and unfortunately often only spoken in accidental remarks,) is by no means so well known as it would have been, had he printed all his stores of geological knowledge in consecutive form. All that I know of this subject with respect to these Cretaceous formations, is in the first

[232 Physical Geography.]

instance derived from him, subsequently aided by personal observation on the ground.

The story revealed by these various strata is this: When, after the temporary upheaval of the Lower Greensand, the land gradually sank in part beneath the sea, it happened that the Upper Greensand was being deposited far in the west on a sea-bottom that now forms an eastern part of Devonshire. Not far from its margin, a fragment of the old greater land, in our day known in a modified form as the granite hills of Dartmoor, stood high above the level of the sea, and at the same time, on the opposite side of what is now the Bristol Channel, Wales also formed high land. The pebbly shore of the lower land near Dartmoor, has long ago been destroyed by denudation, but the sediments laid down not far from the shore still exist in the coarse sandy strata that form the Upper G-reensand west and east of the river Exe. As we go eastward from that area towards Devizes, the Upper Greensand still continues to be comparatively coarse, and by degrees in Buckinghamshire, and Bedfordshire, and on into Cambridgeshire, it gets finer and finer, and at length becomes white, calcareous, and marly, and, as it were, seems to mingle with the Gault beneath and the Chalk above, and the Gault, indeed, in a lithological point of view, sometimes seems to disappear altogether.

In like manner, at the western end of the Wealden area, and along the base of the South and North Downs, the Upper Greensand for many miles consists of fine, white sand, and in the Malm-rock is somewhat chalk-like and calcareous, till going further east towards Folkestone, it gradually becomes untraceable as a special formation, and merges into the underlying Gault and the overlying Chalk.

[Physical Geography. 233]

The meaning of this is, that distinct coarse Upper Greensand strata were deposited not far from shore in the west, gradually getting finer towards the east, because the finer and lighter material was drifted further from shore. At the very same time, in the farther east of what is now England, the sediments were still finer, and depositions akin to Chalk, and even the Chalk itself, had begun to be formed in a deeper sea, far removed from land, so that according to this view, part of the lowest strata of the Chalk, in the eastern and southeastern parts of England, were deposited contemporaneously with the coarse Upper Greensand of eastern Devonshire. On no other hypothesis that I know than this of Godwin-Austen's, can the phenomena connected with the Gault, Upper Greensand, and the lower strata of the Chalk, be rationally accounted for, and I believe that hypothesis to be true.

The upper strata of the Chalk consist of nearly pure chalk with lines of flint, and as it accumulated, the sinking of the western and northern fragments of the old continent steadily continued, till at length they almost, if not entirely, sank beneath a sea, broad and silent, except when roused by storms, like the Atlantic of our own time, for though the Echini and shells found in our chalk, show that the sea of those days was not so deep as the present Atlantic, yet the prevalence of prodigious numbers of Globigerina and other Foraminifera shows that the old and the new seas are akin in the nature of their organic sediments. If the whole of the older land was not submerged, (making an allowance for the lowering of the mountain lands by subsequent subaerial waste,) even then we can only suppose that a few insignificant islets rose above a waste of waters, that spread not only over Britain, but also

[234 Physical Geography.]

over a very large part of the Europe of the present day, long before the Alps and the Pyrenees rose into mountain chains, and only a few islands formed of Palæozoic rocks stood above the waves. This surely was a striking phase of an older physical geography, which affected areas far wider than Europe alone, but which in the course of time came to an end in a manner which we shall presently see. To do so thoroughly we must consider the rocks of the continent for a little.

A vast lapse of time took place between the close of the deposition of the uppermost Cretaceous strata of England, and the commencement of the deposition of the succeeding Eocene formations, for in England we have no deposits of intermediate age. What, however, helps to prove this great hiatus is, that on the Meuse, at Maestricht, there is a calcareous formation about 100 feet thick, which lies unconformably on the Chalk, the line of unconformity being marked by a line of water-worn flint pebbles. Some of the fossils are of the same species with those found in the Chalk, and Cephalopoda of the genera Baculites and Hamites, not yet known in strata younger than the Cretaceous rocks of Europe, are found in the Maestricht beds. On the other hand, Volutes, and other genera of Tertiary type, are found in the strata, so that this marine fauna may be said to be of a type intermediate to those of the Cretaceous and Eocene epochs.

Extending for great distances round Paris, there are numerous small patches of pisolitic limestone, once united, but now separated by denudation. These contain some Cretaceous species, but many others are more Eocene than Cretaceous in their affinities.

At Faxoe also, in the Isle of Seeland, in Denmark, there is a yellow limestone so full of corals that it was

[Physical Geography. 235]

probably a coral reef. It contains among other shells many univalves which are unknown or rare in the Chalk, such as Cyprœa, Oliva, &c., and along with these Baculites and Belemnitella, both unknown in European Eocene strata, though the latest intelligence from Australia tells of a Belemnite in certain late Tertiary strata there. Overlying the common white Chalk, this Faxoe formation by its fauna also seems to be intermediate in date to the ordinary Cretaceous and Eocene strata.

But without such data as these it is evident to any reflective mind, that a great gap in time, unrepresented by any sedimentary formations in England, took place in our area between the deposition of the latest bed of English Chalk, and that of the earliest Eocene stratum, for, excepting a few Foraminifera, the species found in the Chalk seem all to have been remodelled before our Eocene epoch began, in so far that palæontologists recognise none of the species as identical, and before the days of Darwin they would generally have been spoken of as new creations.