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diameter, which are found at Horstead, Sherringham, 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:
Chalk-rock, a thin hard cream-coloured bed with green-coated nodules, about
Chalk-without-flints, or with a very few flints in the uppermost
Totternhoe stone, generally two layers, of hard and rather brownish sandy chalk, with dark grains
Chalk marl with stony layers.
400 to 500
The Totternhoe stone has been largely quarried for building-purposes and to be burnt for lime. 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 Cups (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).
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 flintless beds 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. also identified the Chalk-rock in places in Dorsetshire and Devonshire.
On the Dorsetshire const 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 fossils locally developed there:
Upper Chalk. 250 feet.
Middle Chalk. 75 feet.
(PURLEY BEDS, with layers of flint nodules and thin tabular flint, Micraster cor-anguinum and Inoceramus Cuvieri. UPPER KENLEY BEDS, with layers of flint, nearer together than in above division, Micraster cor-anguinum, Ananchytes ovatus, Spondylus spinosus.
LOWER KENLEY BEDS, with flints wider apart, Holaster
WHITELEAF BEDS, with few or no flints, Inoceramus
UPPER MARDEN PARK BEDS, without flints, Ammonites
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.
upper beds of the Chalk contain very few nodular flints, so that the bedding is not well shown: sometimes thin layers of flint fill the narrow vertical openings of the even joints. These beds he calls the Margate Chalk; they have a thickness of about 80 feet. Below, the series called the Broadstairs Chalk is distinguished by containing layers of tabular and nodular flint. The Margate Chalk contains fossils identical. with those of Norwich, where the upper beds have been compared to the Chalk of Maestricht in Holland and Faxoe in Denmark, in which countries the Chalk exhibits gradations into the Tertiary strata above.
An excellent description of the Chalk of Dover was published many years ago by William Phillips, and the following Table shows the chief divisions which he made; to these are appended some local names and the palæontological zones determined by Prof. Hébert :
One of the most interesting discoveries in the Chalk was that of a Granitic boulder at Purley near Croydon, described by Mr. Godwin-Austen. It was originally about 3 feet long, and was accompanied by some decomposing fragments of a felspathic rock and with a compact mass of siliceous sand. Mr. Godwin-Austen considered that an ice-floe was the agent by which alone such a block could have been lifted from the coast and conveyed far out to sea.
At Grays Thurrock the thickness of the Chalk is upwards of 660 feet at Harwich it was proved to be 888 feet, and at Kentish Town 640 feet. (See fig. 19, p. 257.)
These names were given by Mr. G. Dowker.
Economic Products, &c., of Chalk.
The Chalk Downs produce a scanty herbage, to which sheep are largely devoted.
In some parts good crops of barley, turnips, and wheat are produced. The Lower Chalk and Chalk Marl are, as a rule, more fertile than the Upper Chalk. The ponds generally require to be clayed.
The Chalk Downs are considered to retain their ancient character more than any other tracts of country. Beech trees grow exceedingly well on the Chalk where covered with clay-with-flints or brickearth, and in Buckinghamshire they are largely used for Chair-making.
In many places there is no durable stone save the scattered 'Sarsens.' In other places, as before mentioned, hard beds have been worked for building-purposes.
The flints are largely used for road-metal and for buildingpurposes. When burnt and ground they are employed in the manufacture of china, porcelain, and flint-glass.
Gun-flints in former times were largely manufactured from the chalk-flints, and are still made at Brandon and Norwich for export to Africa.
The Chalk pits vary from 50 to 150 feet in depth. The men work at the top of the pits with levers (or where the chalk is very hard, with gunpowder), and throw the Chalk down in great masses, which break to pieces in their fall. The joints are taken advantage of in excavating the Chalk.
The Chalk is extensively burnt for lime: it is also prepared for whiting at Grays, Kintbury,3 and other places.
1 These will be described in the sequel.
2 The most remarkable blowing up of Chalk took place some years ago at the Round Down Cliff, Dover, when hundreds of tons were thrown into the sea to make an opening for the railway beneath the cliff.
The whiting is prepared by grinding the soft Upper Chalk, dug on the spot, to a fine pulp with water, and allowing the whole to flow into