CHALK FORMATION'. 



< HAI.K FORMATION*. 



The thickness of thU series near Folkstone U from 25 to 30 feet : 

 at Oodstone it increases considerably, and the depth of the well* 

 sunk through it in the Malm-Kock strata of Hampshire varies from 

 60 to 100 feet In Western Sussex the thickness i. between 70 and 

 80 feet It is about 70 feet in the Isle of Wight. The thickness of 

 the Oreensand at Black Down i* about 100 feet, probably from 00 to 

 80 feet in the Vale of Wardour, and from 80 to 60 feet near Swin.l.m. 

 At Cambridge it u not more than 18 inches; thence through West 

 Norfolk the stratum U nowhere distinctly seen. At Huniitanton 

 the beds which are supposed to represent it are not more than 2 feet 

 thick. 



Gault The stratum which is usually found between the Upper 

 and Lower Oreensand U obscured at Kant Wear* Bay by the ruing 

 of the superior beds, but is visible in detached point*. Kartlu r <>n. 

 towards Folkstone, it become* more marked, and forms the greater 

 part of the cliff at Copt Point, as well as the grassy cliff between 

 the base of the Hartello tower, situated in the vicinity, and the sea. 

 Thence it forms a narrow bond between the Upper and Lower Green- 

 land. Near Oodctone it occupies a tract distinguished as ' the Black 

 Land,' and forms a slight depression below the stratum which affords 

 the Arestone. Between Farnham and Alton this narrow belt of 

 Oault swells out to three or four times its former width, and then 

 again narrowing, continues to form a narrow band between the two 

 strata of Qreensand aa far as Beachy Head. In the Isle of Wight 

 this stratum likewise forms a narrow band between the Upper and 

 Lower Qreensand. The Qault again appears in the Vale of \\ ardour : 

 on the south it forms a rapid slope ; on the north a depression imme- 

 diately below the sand. It is here identified with that in the eastern 

 counties by the characteristic fossils. At Ridge, near Funthill Park, 

 the clay of this stratum has been long used for tile-making, and it is 

 there 75 feet in thickness. From the Vale of Wardour, and thence 

 north-eastward to the sea at Hunstanton, the Oault everywhere 

 appears, though it is much reduced in quantity in Norfolk. This 

 stratum occupies a large part even of the higher grounds between 

 Whitchurch and Wing. Immediately to the west of Hitchin and 

 Baldock it is still wider; the towns of Shefford and Biggleswade 

 stand on it. From Cambridge, for a few miles towards the north, it 

 likewise occupies as great a width. In consequence of the numerous 

 borings for water made in Cambridgeshire about this part, its relations 

 nnd thickness have been well ascertained, especially from Baaingbourne 

 through Meldrith, and thence towards Cambridge. ThU stratum is 

 very distinct at MUdenhall : the Blue Oault has been traced as far 

 as West Newton, about three miles south of Ingoldsthorpe. The 

 valley between the Chalk and Lower Greensand is there interrupted 

 by an advance of the Chalk ; and beyond that point the Blue Oault 

 is no longer observable : its place is thence occupied by the red 

 marly stratum of Hunstanton Cliff, which in a calcareous argillaceous 

 matter, 4 feet thick, and it is questioned by geologists whether the 

 term Oault should be applied to it The Oault, as far as regards its 

 composition, may be divided into two portions : the upper port, 

 immediately succeeding the Upper Greensand, contains green particles, 

 and thence for some feet downwards it is harsh and sandy. The 

 lower portion consists of a smooth uniform very plastic clay, of a 

 light-blueish colour, which is used for tiles and common pottery. 

 Throughout the Oault, but chiefly in the lower part, concretions of 

 iron pyrites are found, and other nodules and irregular masses. The 

 thickness of this stratum at Copt Point is about 130 feet At 

 Merstham it U 150 feet thick, which is likewise the average thickness 

 in Cambridgeshire. In the Isle of Wight it is about 70 feet ; at 

 Ridge about 75 feet ; near Thame 90 feet ; at Mildenhall the blue 

 clay is only 9 feet Mr. Rose considers it not more than 15 feet in 

 West Norfolk. 



The Lower Greensand. 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. The resemblance in the aspect of the surface 

 of the country, here occupied by the Lower Oreensaud, to that of 

 the Black-Down Hills, in Devonshire, is extremely striking; and 

 perhaps indicates that the description of the latter more properly 

 belongs to this section than to that which treats of the Upper Green- 

 sand stratum. The Lower Greensand has three distinct subdivisions, 

 clearly denned in most parts where it occurs. This series of strata 

 rises gradually from Copt Point, and occupies the whole cliff west of 

 the Tillage; thence it is continued without interruption through 

 Snodgate, and in the heights above Hythe. It* outcrop turns from 

 the coast to the interior at Adliugton Corner ; here the subdivisions 

 are all distinctly marked, and their respective limits defined. The 

 lower bods, which contain much calcareous matter, are extensively 

 worked in quarries, both for building and lime-burning, at I'liickloy, 

 on the north-west, and at Great Chart, on the south-west of Ashford ; 

 and generally along the outcrop west of Adlington Comer, where it 

 forms a prominent ridge adjoining the valley of the Weald : here 

 are the principal beds of stone known under the name of ' Kentish 



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 K> nt i-h 

 rag. From Adlinjjtoa Corner the Lower Greensand continues towards 



the west in a broad band varying in width ; on the coast the distance 

 from the Chalk at Folkstone Hill to the ouU-rop ,.f this series is about 

 10 miles, but from Lenham to the outcrop it is not more than 2 

 miles. Haidstone, Sevenoaks, Oodstone, Rejgate, Dorking, and <:...!., I - 

 ming stand on the Lower Greensand aeries. Near Godstone the 

 surface is comparatively lower, and ponds are frequent where the 

 middle stratum occurs ; the stony beds of the lowest group then rise 

 to form the escarpment of Tilbuntow Hill, which is nearly on a 

 level with the Chalk Downs. At the top ( t In- hill, the beds, which 

 to the north of Tilburstow Hill rise uniformly at an anirle of not 

 more than 10 degrees, are suddenly thrown up to about 45 degrees, 

 giving decisive evidence of an elevation fn.in tin- Chalk, or 

 sinking towards it Fullers' Earth has been dug in tli ur.-y 



for a very long period; at present the neighbourhood of Nut: 

 the only place in which it is got The beds occur near the top of 

 the lowest stratum of Oreensand ; in one pit near Nutfield tlu- prin- 

 cipal bed of Fullers' Kurth is 10 feet thick. On the south of the 

 Hog's Back the Lower Oreensand 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. llindhcad isthemostproinii.i-ut 

 point in this part of the country, where the whole of the 

 occupied by the Lower Greeusand is wild and barren, producing only 

 fern, heath, and fur/e. 



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 t i,,- 

 Weald. At Beachy Head it is three milks wide, but it in only one mile 

 wide a little to the west of the spot where the Adur runs through it. 

 The Lower Oreensand 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 Oreensand crossing the 

 island from the shore on the south of Beinbridge-Down to the foot 

 of Afton Down. The sands likewise form the lower ground of 

 the interior from Mottestoue through Newchurch to the coast 



A narrow belt of Oreensand runs along the west and north-west 

 of Dorsetshire. In the Vale of Wardour the Lower Greensand is 

 nowhere prominent ; but it occupies the whole of the entrance of tin- 

 Vale of Pewsey, and continues with its subdivisions well 

 through the northern counties in a north-east direction as far 

 coast of Norfolk. The greatest width of the formation in this part. 

 occurs between Leighton and Ampthill in Bedfordshire, where it 

 rises in Bow-Brickhill to the height of 683 feet above the sea. 

 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 lst 

 quality is in a bed from seven to nine feet thick. The pits in this ].art 

 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 

 Cretacean 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 on 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 ill Bonn , 

 North America. In South America deposits of this period hav, 

 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 plants : 

 /nfmoria. Sponges, Zoophyt /'rmata, Mottutca, Citutacta, 



Fishes, and Reptiles. Sir Henry De La Beche observes, that 

 "Organic remains are in general lieautifnlly 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 exuviie 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. [FLINT.] 



Although the remains of plants arc rare in this formation i-i 

 England, they have been found in abundance in the coirU-mpoi. 

 sandstones of the continent of Europe. Amongst them have been 

 found the remains of dicotyledonous plant*. 



An examination of the flints by the microscope reveals tin- 

 existence of many forms of Diatomaceas in the Chalk. From the 

 siliceous structure of their frustules these organisms are entirely 

 preserved wherever they occur. A large number of species have 

 been discovered in the Chalk. [DIATOMACKX.] 



Amongst the lowest animals we must now reckon the / 

 which were formerly regarded as minute <', r /ni/,,j,i,,l,i by D'Orbigny. 

 Many forms of these creature - m to hold a place !> 



