The Lower Greensaud.— This stratum appears of a uniform surface, shooting out beyond the Chalk in the south-east counties, And occupies a much larger area than either of the upper strata of the Greensand series. Tho resemblance in the aspect of the surface of the country, here occupied by the Lower Greensand, to that of the Black-Down Hills, in Devonshire, is extremely striking ; and perhaps indicates that the description of the latter moro properly belongs to this section than to that which treats of the Upper Green sand stratum. The Lower Greensand has three distinct subdivisions, clearly defined in most parts where it occurs. This series of strata rises gradually from Copt Point, and occupies the whole cliff west of the village ; thence it is continued without interruption through Sandgete, and in the heights above Ilythe. Its outcrop turns from the coast to the interior at Addington Corner ; here the subdivisions are all distinctly marked, and their respective limits defined. The lower beds, which contain much calcareous matter, are extensively worked in quarries, both for building and limo-burning, at Pluckley, on the north-west, and at Great Chart, on the south-west of Ashford ; and generally along the outcrop west of Addington Corner, where it forme a prominent ridge adjoining the valley of the Weald : here are the principal beds of stone known under the name of 'Kentish Rag.' Extensive quarries are worked at Boughton, to the south of Maid stone. The stone for the construction of Westminster Abbey is said to have been procured here. The stone is a variety of the Kentish rag. From Adliogtoa Corner the Lower Grecnsamd continues towards the west in a broad band varying in width ; on the coast the distance from the Chalk at Folkatonellill to the outcrop of this series is about 10 miles, but from Lenham to the outcrop it is not more than 2 miles, Maidstone, Sovenoaks, Codstone, Reigate, Dorking, and Godal ming stand on the Lower Greensand series. Near Gocistone the surface is comparatively lower, and pond)] are frequent where the middle stratum occurs ; the stony beds of the lowest group then rise to form the escarpment of Tilburetow 11111, which is nearly on a level with the Chalk Downs. At the top of the hill, the beds, which to the north of Tilburstow Hill rise uniformly at an angle of not more than 10 degrees, are suddenly thrown up to about 45 degrees, giving decisive evidence of an elevation from the Chalk, or of a sinking towards it. Fullers Earth has been dug in this part of Surrey for a very long period; at ,resent the neighbourhood of Nutfield is the only place in which it is got. The beds occur near the top of the lowest stratum of Greensand; in one pit near Nutfleld tho prin cipal bed of Fullers' Earth is 1G feet thick. On the south of the Flog's Back the Lower Greensand rises, like the Chalk, at a very high angle, and then, being bent suddenly in an opposite direction, is continued several miles to the south. Ifindhead is the most prominent point in this part of the country, where the whole of the tract occupied by the Lower Greensand is wild and barren, producing only fern, heath, and furze.
As this formation turns towards the east and continues along Sussex to the coast, it is not nearly so wide as on the north of the Weald. At Beachy Head it is three miles wide, but it is only one mile wide a little to the west of the spot where the Adur runs through it. The Lower Greensand occupies a great part of the surface on the south of the Isle of Wight, and is everywhere conformable to the Chalk, a ridge of highly-inclined strata of Greensand crossing the island from the shore on the south of Bembridge-Down to the foot of Afton Down. The sands likewise form the lower ground of the interior from Motteatone through Newebureh to the coast.
A narrow belt of Greensand runs along the west and north-west of Dorsetshire. lu the Vale of Wardour the Lower Greensand is nowhere prominent ; but it occupies the whole of the entrance of the Vale of Pewsey, and continues with its subdivisions well defined through the northern counties in a north-east direction as far as the coast of Norfolk. The greatest width of the formation in this part occurs between Leighton and Ampthill in Bedfordshire, where it rises in Dow-Brickhill to the height of 6S3 feet above the sea. Near Woburn there is a fullers' earth pit, the beds of which occur, like those in Surrey, near the top of the lowest division ; that of the best quality is in a bed from seven to nine feet thick. The pits in this part of the country have continued to supply fullers earth for more than a hundred years.
The three groups into which this stratum is divided are, in most places in the south-east counties where sections have been made, well defined; and in 'general, in different situations where this formation occurs, the respective characteristics are found to be alike. The Cretaeean System is not confined to England, but is found extending over very large portions of the continent of Europe. It is seen in France on the coasts opposite to England, and it is found ou the north as far as Denmark. It may in fact be traced from the north east of Ireland to the borders of Asia Minor, and from Denmark to the south of France. It also has its representative in some parts of North America. In South America deposits of this period have also been developed along the whole country from Columbia to Tierra del Fuego. The south-east of India has also yielded fossils, which apparently belong to this period.
The organic remains in the Chalk and Greensands are usually abundant, and are mostly marine. They consist of marine pints Infasoria, Sponges, Zoophytes, Echisodersueta, Atollucaca, Crnetacea, Fishes, and Reptiles. Sir Henry Dc La Beebe observes, that "Organic remains are in general beautifully preserved in the chalk ; substances of no greater solidity than common sponges retain their forms, delicate shells remain unbroken, fish even are frequently not flattened, and altogether we have appearances which justify us in concluding that since these organic exuvite were entombed they have been protected from the effects of pressure by the consolidation of the rock around them, and that they have been very tranquilly enveloped in exceedingly fine matter, such as we should consider would result from a chemical precipitate." The most remarkable form in which the fossils of this formation appear is that of flint. The production of this substance has by sonic been referred to organic agencies. [FLixr.) Although the remains of plants are rare in this formation in England, they have been found in abundance in the contemporaneous sandstones of the continent of Europe. Amongst them have been found the remains of diootyledonous plants.
An examination of the flints by the microscope reveals the existence of many forms of Diatornacem in the Chalk. From the siliceous structure of their frustules these organisms are entirely preserved wherever they occur. A largo number of species have been discovered in the Chalk. [Thsvomsces::.] Amongst the lowest animals we must now reckon the Poramingcra, which were formerly regarded as minute Ceplialopoda by D'Orbigny. Many forma of thous creatures, which seem to hold a place between the Sponges and some of the Injusoria are found in the Chalk. [FORAMINIFERA.) Of the Zoophytes, the Poly:0a have been found in the greatest abundance in the Cretaceous beds (Neocomien) of the continent of Europe. They have been most elaborately described by D'Orbigny. [PoLvzok.] The Echinodermata abounded during the period of the deposit of the Chalk, and afford a larger number of interesting forms than occur in any other formation. The genus Marsupitcs affords an instance of the passage amongst these creatures from Encrinites to the Spatangi. Numerous species of Spatangus, Cidaris, Goniaster, and other genera of this family are found. The spines of the Echinidx are often found separated from the shell. [ECHINODERMATA.] Several forms of Crustacea belonging to the more highly-developed sections of the family are found.
The Mollusca are abundant. Of these the forms of Brachiopoda, especially Terebratula, are numerous. The genus Rudistes, which D'Orbigny refers to the Brachiopoda, is in some respects the most interesting of the Mollusca of the Cretaceous Formations. The species are most abundant in the Cretaceous series of the South of Europe. The Cephalopodous Mollusca were very numerous and varied in their forms during the Cretaceous period. The following genera are found :—Nautilus, Ammonites, Crioceratites, Turrilites, Scaphites, Bacutites, Ha mites, and others.
The Fishes of the Cretaceous system are numerous, and belong to the Placoid, Ganoid, Ctenoid, and Cycloid types. Of the last two the genera are fewer in number than of the first two. The Ctenoids and Cycloids however appear in the Cretaceous system for the first time, and are interesting on this account.
The Reptiles, though not so numerous in the Cretaceous period as in that which immediately preceded it, are nevertheless numerous. It is here that the Mosomurus has been found, also several species of Pterodactyli, and the remains of the iguanodon and Ichthyosaurus, with species of Chelonia.