It constitutes the foundation of the greater part of Norfolk and Suffolk, but is in these counties very much concealed by Glacial Drifts, and does not there appear in such conspicuous bills as those which extend from Royston in a south-westerly direction, forming the Royston and Luton Downs, the Chiltern Hills, the Marlborough Downs, and Salisbury Plain. Thence the Chalk stretches out irregularly to the west beyond Dorchester, and is found in outliers near Chard, Seaton, and Sidmouth. Eastwards of Salisbury Plain the Chalk forms a large extent of Hampshire, it is found in the Isle of Wight, and borders the Wealden district, forming the cliffs from Margate to Folkestone on the north, and those from Beachy Head to Brighton and Little Hampton on the south. It is also exposed at Gravesend and Grays Thurrock.

In Yorkshire the following succession of the Chalk strata has been determined by Professor Phillips :Upper Chalk, rich in Spongiade, Marsupites, &c.

100 Middle Chalk with flints, and few fossils

. 400 Chalk Lower Chalk, with few fossils Red and Grey Chalk, with many fossils .

40 Red Chalk, Belemnites Listeri, &c.

30 He observes that the unconformability of the Chalk to all the strata beneath it is a striking feature of the geology of Yorkshire. The lowest bed of Red Chalk is the equivalent of the Hunstanton Limestone.

Mr. Judd has pointed out in regard to the Chalk of Lincolnshire, that the occurrence of the flint layers is very irregular. Above the Chalk Marl is a considerable thickness of hard Chalk (as in Norfolk) which has been used for buildingpurposes. Louth Abbey was in great part constructed of it. Near Louth this series contains a well marked bed of Red Chalk, 5 or 6 feet in thickness, and some other bands of a pinkish hue, all distinct from and much above the Hunstan

Feet

100

.

6

ton limestone. The “Sponge-bed' with Spongia paradocica is found at the base of the Chalk series, graduating into the Hunstanton limestone. The Wolds of Lincolnshire are much more covered with superficial deposits than the downs of the south of England, or even Norfolk; hence the district of the Chalk in this county does not present that uniformly bare and arid appearance so characteristic of it in most parts; in fact, nearly the whole of it has now been brought under the plough, and with the most satisfactory results.

In Norfolk the Chalk was divided by Mr. Samuel Woodward into :

Upper Chalk, with flints.
Medial Chalk, with few flints.
Lower or Hard Chalk.
Chalk Marl.

The thickness of the Chalk-with-Aints (Upper and Medial) was proved to be 1,050 feet in a well-boring at Messrs. Colman's at Norwich ; and that of the Chalk-without-flints (including the Hard Chalk) 102 feet. The Chalk Marl is only about 3 feet in thickness, and it is in a bed of white Chalk occurring at the base of it at Hunstanton that the Spongin puradoxica is found: this bed, called the Sponge Bed, is scarcely 18 inches in thickness, and may represent the Upper Greensand.' (See p. 238.)

The Hard Chalk has been much used for building-purposes. It has been largely quarried at Stoke Ferry and Whittington; it has yielded Ichthyosaurus campyloilon; also Ammonites peramplus, and A. Austenii, each about 2 feet in diameter.

The Upper Chalk (very rarely the Medial Chalk) is characterized by the presence of the gigantic flints termed paramoudras or potstones, often 3 feet in length and 1 foot in diameter, which are found at Horstead, Sherringbam, Thorpe, &c. Remains of Leiodon anceps, a Lacertilian reptile allied to Mosasaurus, have been obtained by Mr. T. G. Bayfield at Lollard's Pit, Norwich. But the very highest beds of chalk known in Norfolk are those which occur at Trimmingham, and which contain fossil sponges in the flints, only found elsewhere in the coarse flint-gravel which caps Mousehold Heath, near Norwich. (See fig. 21, p. 287.)

Mr. Whitaker has thus divided the Chalk of Buckinghamshire and neighbouring counties :

Feet 300

ܙ

.

Chall:-with-flints
Chalk-rock, a thin hard cream-coloured bed with green-coated
nodules, about

4 Chalk-without-flints, or with a very few flints in the uprermost part

400 to 500 Totternhoe stone, generally two layers, of hard and rather brownish sandy chalk, with dark grains

6 Chalk marl with stony layers .

80 The Totternhoe stone has been largely quarried for building-purposes and to be burnt for Jime. It is a waterbearing stratum ; springs are thrown out at its base.

In Oxfordshire and Berkshire the thickness of the Chalk is pretty much the same as in Buckinghamshire; the Chalkrock being from 6 to 12 feet.

In Wiltshire the total thickness of the Chalk is about 800 feet. According to Prof. Buckman the Chalk Marl (rich in Ammonites) varies in thickness from 20 to 50 feet, and generally throws out the springs of the Chalk, but these often become dry in summer: hence the names Winterbourne Basset, Winterbourne Monckton, &c., which have been given to the villages in the district.

Lyell has noticed that some of the pear-shaped masses of flint often resemble in shape and size the large sponges called Neptune's Cuis (Spongia patera), which grow in the seas of Sumatra. Mr. F. Kitton has advocated the spongeous origin of flints.

In Dorsetshire the Chalk has been divided by De la Beche into:

Chalk-with-flints (146 feet).
Chalk-without-flints.
Chalk-with-quartz-grains.

The Lower beds of the Chalk are very nodular. Here, indeed (as Mr. Whitaker remarks), it is often hard to mark the junction; the Chalk gets darker, and harder, until it seems almost one mass with the Greensand. At the mouth of the Axe, the bed with quartz-grains is about three feet thick, and contains fossils.

Westward of Seaton the famous Beer Stone is met with. It consists of a series of beds of tolerably hard chalk, about 12 feet in thickness, the whole resting on the Greensand. Its occurrence is local, but this fact is significant as showing the variable nature of the Chalk. The bed has been worked, or rather mined, for very many years; portions of Exeter Cathedral were built of it.

There is no hard line anywhere in the Chalk series : the Aintless bels appear to attain a maximum thickness of at least 50 feet, and the Chloritic Marl, the rich fossiliferous bed, forms the true base of the Chalk and is most properly included with it.

Mr. Whitaker has noticed the overlap of the Upper Chalk-with-flints on to the Greensand at Beer Head. He also identified the Chalk-rock in places in Dorsetshire and Devonshire.

On the Dorsetshire co:ust east of Weymouth the Chalk is very much disturbed, the bedding being in some places vertical or even reversed. The thickness near Weymouth is estimated at 800 feet.

In the Isle of Wight Mr. Charles Barrois has identified the following palæontological divisions which were established by Prof. E. Hébert in the north of France :

At Culver Cliff the Chalk dips at a very high angle, and on the opposite side of the Island, at Alum Bay, it is nearly vertical. (See fig. 20, p. 274.)

In Surrey the Chalk is from 350 to 500 feet in thickness. Mr. C. Evans has divided the Chalk near Croydon and Oxtead into stages according to the zones of fɔssils locally developed there :

{PURLEY BEDs, with layers of flint nodules and thin tabular

flint, Micraster cor-anguinum and Inoceramus Curieri. Upper UPPER KENLEY BEDS, with layers of flint, nearer together Chalk. than in above division, Micraster cor-anguinum, Anan250 feet. chytes ocatus, Spondylus spinosus.

LOWER KENLEY BEDs, with flints wideř apart, Holaster

planus and Micraster cor-boris. Middle Chalk.

WHITELEAF BEDS, with few or no flints, Inoceramus 75 feet.

Brongniurti, and Galerites albogalerus. Lower

UPPER MARDEN PARK BEDS, without flints, Ammonites Chalk,

peramplus, and Inoceramus mytiloides. 190 feet?

LOWER MARDEN PARK BEDS, grey chalk and chalk marl,

with Ammonites varians, Belemnitella plena. In East Kent the thickness of the Chalk has been estimated at upwards of 800 feet.

In the Isle of Thanet, as described by Mr. Whitaker, the

1 This bed is called the 'Craie glauconieuse' by Prof. Hébert; but as the Chloritic Marl is glauconitic, the term Chalk Marl seems preferable, more especially as a nodular bed, found at the base of the chalk with Inoceramus labiatus, is regarded as corresponding to the Totternhoe stone which Mr. Whitaker places at the top of the Chalk Marl.