large part of Northamptonshire and in Oxfordshire. In Oxfordshire he observes that the Upper Estuarine series is traceable to the Stonesfield Slate, and the difficulty of separating the two Estuarine series led formerly to the Northampton sand (Lower Estuarine) being regarded as the equivalent of the Stonesfield Slate. Among the fossils are species of Pholadomya, Modiola, Ostrea, Cyrena, Unio, &c.; remains of Cetiosaurus also occur in the beds.

All the characters presented by the Upper Estuarine series, according to Mr. Judd, point to the conclusion that they were accumulated under an alternation of marine and freshwater conditions, such as occurs in the estuaries of rivers.

In the north-western part of Lincolnshire the Rev. J. E. Cross has described clayey beds about 40 feet in thickness as resting upon the Lincolnshire limestone. They contain Ostrea subrugulosa, &c.; also fish-remains.

The Clays in this series are worked for brick-making. The soil is comparatively barren.

GREAT OOLITE.

The Great or Bath Oolite consists of a series of shelly limestones (rags) and fine oolites or freestones, often exhibiting much false-bedding, and generally of a yellowishwhite colour.

The Great Oolite is rich in univalve mollusca, such as Alaria, Cylindrites, Nerinæa Voltcii, Nerita, Patella rugosa, Purpuroidea Morrisii ; amongst the bivalves are Ceromya, Cypricardia, Gervillia, Trigonia costata, Pholadomya, Tancredia brevis, Astarte excavata, Arca, Ostrea gregarea, Pecten lens, Lima cardiiformis, and Opis lunul'atus. Cephalopoda are not abundant. Amongst the

Feet

.

.

Brachiopoda are Rhynchonella concinna, Terebratula perovalis, T. digona, &c. The Coral, Eunomia radiata, is common near Bath.

The Great Oolite series in the neighbourhood of Bath was thus divided by Lonsdale :

(1. Coarse, shelly limestones Upper Rags. 2. Tolerably fine oolites

20 to 55 (3. Tough, brown, argillaceous limestone Fine freestones.

10 to 30 Lower rags, Coarse, shelly limestones

10 to 40 The Bath stone, as is well known, hardens on exposure after it has been quarried. In its natural bed it is soft and moist, and Professor Ansted states that a cubic foot of Bath stone will absorb one gallon of water. According to E. Owen, who wrote in 1754, there is no stone that differs so much in its bed, and after it has been wrought and exposed to the air, as the Bath free-stone. While it is in the ground, it is soft, moist, yellowish, and almost crumbly; and it seems very little more than congealed sand, and that not well concreted together. But when it has been some time exposed to the air, and is thoroughly dry'd, it becomes white, hard, firm, and an excellent stone.'

The beds are largely quarried, or mined, near Bath (on Combe, Bath Hampton, and Farleigh Downs), at Box and Corsham.

Some of the beds, called Weather Stones (brown shelly oolitic limestones), are specially valuable for plinths, cornices, &c.; the Scallet is of superior quality, being of very fine texture. The absence of fossils renders the rock more valuable as a freestone.

At Minchinhampton there are extensive quarries (Hampton stone), showing 30 to 40 feet of rock. The beds are also worked at Chalford, Brimscombe, Burley, &c. The soil is a loose stone-brash.

In the district south of Frome the Great Oolite thins away entirely, and is represented partly by the Forest Marble, and perhaps also by the Fuller's Earth.

The Great Oolite generally forms a well-marked feature in Gloucestershire and the borders of Oxfordshire.

At Coln St. Denis the beds, consisting of white limestone resting on marls, have a thickness of about 145 feet. Burford the beds have a thickness of about 100 feet.

The upper rock-bed, according to Mr. Hull, is frequently pierced by Lithodomi, and it also affords interesting evidence of having been consolidated contemporaneously with its deposition. Occasionally he has noticed beds of conglomerate formed by waterworn fragments of the underlying limestone.

On Minchinhampton Common, where the beds have yielded a rich collection of fossils to Mr. Lycett, there appears to be no positive line of separation between the Great Oolite and the Forest Marble.

Other fossiliferous localities are near the Seven Springs, North Leach, Burford, and Sherborne Park (Gloucester

shire).

At Sapperton Tunnel Mr. Hull estimates the thickness of the limestones at 20 feet. He observes that in the country near Woodstock, at Wychwood Forest, &c., the beds are blue when reached at some depth, but they weather white, and are called white limestones. The limestones are not usually colitic, but compact and sometimes marly. The beds contain plant-remains and jet, and have a thickness of from 20 to 30 feet.

1 Mr. Judd has pointed out that when dug at great depths or otherwise obtained at points where they have not been exposed to atmospheric influences, all the Oolitic rocks exhibit an almost uniform deep-blue tint, which is apparently communicated to them by a diffusion through their substance of small quantities of sulphide of iron.

Great Oolite Limestone.

25

The term Great Oolite Limestone is used in Lincolnshire and the northern part of Northamptonshire because the Great Oolite series is divided into :

3. Great Oolite Clay, about 20 feet in thickness.
2. Great Oolite Limestone

1. Upper Estuarine series (Stonesfield Slate). The Great Oolite Limestone, as described by Mr. Judd, consists of alternate beds of white limestone and marly clay, with seams made

up

of the shells of small oysters. Volitic structure is seldom developed.

Among the fossils are Ostrea subrugulosa, 0. Sowerbyi, Homomya gibbosa, Terebratula maxillata, Rhynchonella concinna, Clypeus Mülleri, Isastrea, also bones of Cetiosaurus, and some fish-remains.

Near Banbury, according to Mr. Beesley, it is a white compact earthy limestone, often blue within, and seldom oolitic in structure; moreover, it never assumes the character of a freestone. It is chiefly used as limestone and road-metal. The compact limestones are sparingly fossiliferous, but the intervening shaly or marly beds afford a number of species, many of which have been obtained at Tadmarton.

In Northamptonshire the limestone beds are worked for building-purposes and lime-burning, at Kettering, Higham Ferrers (Stanwick Ragstone), &c.

At Alwalton, near Peterborough, the stone takes a good polish, and is termed the Alwalton Marble. Flaggy beds occur also at Alwalton, Castor, &c.

a

Great Oolite Clay.

This clay, termed Blisworth Clay by Mr. Sharp, and Great Oolite Clay by Mr. Judd, occurs at the top of the Great Oolite series in Northamptonshire, resting upon the white marly limestones (Great Oolite Limestone). Mr. Sharp has estimated its thickness at from 2 to 20 feet. He considers that the clay is not represented in Yorkshire, but doubtless answers to the Forest Marble and Bradford Clay of the southwest of England.

Mr. Judd describes it as a series of variegated, blue, green, yellow, and purplish clays, often containing bands of irregular whitish or pale-green calcareous concretions, and sometimes septaria.

It contains Ostrea subrugulosa, 0. Sowerbyi, Placunopsis socialis, &c. In part the beds seem to be of estuarine character.

The clay is employed for brick-making at Bedford Purlieus, and New England, near Peterborough. At Bottlebridge, near Overton Longville, some ironstone has been raised. The soil is by no means fertile.

FOREST MARBLE.

The Forest Marble, so termed by William Smith from · the Forest of Wychwood in Oxfordshire, consists of flaggy or

fissile oolite, shelly limestone, and beds of clay, sand, and grit, displaying much false bedding. Prof. Hull remarks that owing to the rapid enclosure of Wychwood Forest many quarries have been opened, showing the lower beds (resting on the Great Oolite) to consist of false-bedded shelly oolite, splitting into slabs and flags, and composed of enormous quantities of broken oyster shells; they are about 30 feet in thickness. The higher beds consist of bluish clays and marls, with thin flagstones and roofing slates, from 20 to 30 feet in thickness.