decussata, and Avicula costata

are also characteristic.

Dr. S. P. Woodward obtained more than 100 species of marine animals from this formation in the neighbourhood of Cirencester.

Upper Shale and Sandstone. (Yorkshire.)

UPPER ESTUARINE.

This formation (as described by Mr. Hudleston) is remarkable for the quantity of hard siliceous rock, which is sometimes bedded with it, and sometimes occurs in enormous concretions or doggers'; it occasionally puts on the appearance of a quartzose grit. These doggers are probably the Crowstones' of Young and Bird, who state that of this material several of the ancient rude monuments have been made.

The beds rest on the Limestone series at Scarborough ; under Wheatcroft the thickness is estimated at about 160 feet, and at Gristhorpe 80 feet.

Scarbroite (a hydrous silicate of alumina) occurs in crevices of the rocks.

Some of the clay-beds are worked near Scarborough for manufacture into tiles and drain-pipes.

CORNBRASH.

The Cornbrash consists of pale-coloured earthy and rubbly limestones, which have been well described as often of a pasty or chalky consistency. The beds, where not exposed to atmospheric influences, are mostly compact, blue in colour, and sometimes sufficiently hard to be used for rough buildingpurposes, as near Malmesbury.

The thickness of the formation is about 40 feet.

The fossils include Ammonites Herveyi, A. macrocepha

lus, Ostrea Marshii, Gresslya peregrina, Lima duplicata, Avicula echinata, Myacites securiformis, Terebratula obovata, T. maxillata, T. perovalis, Echinobrissus (Nucleolites) clunicularis, Holectypus depressus, &c.

In the South of England it is never oolitic; it is well developed in Dorsetshire and Somersetshire.

In Oxfordshire, near Woodstock, the Cornbrash, 6 to 15 feet in thickness, consists of shelly limestones. Prof. A. H. Green has noticed that here and there clay-beds occur which cause the formation to swell out to more than double its average thickness; these clays are irregular, and never extend beyond small areas.

The Cornbrash occurs as a rather ferruginous limestone, in the Nene Valley, near Oundle, and Peterborough; here its thickness is about 15 feet. Rushden in Northampton

shire is a noted locality for fossils.

a marly and sometimes

The Cornbrash of Yorkshire is oolitic limestone, overlaid by shale or clays of the cornbrash,' containing Avicula echinata. It is well developed in Newtondale (13 to 14 feet), where (says Mr. Hudleston) its ferruginous character tempted a speculator to work it for iron, while in a secluded nook of the same lovely valley there yet stands (1874) what was meant to have been a colliery-the shaft was sunk to a considerable depth, in the expectation of winning the real north-country coal! The shales vary from 8 to 15 feet in thickness, and seem to form a connecting link between the true Cornbrash and the Oxford Clay.

The Cornbrash is exposed at Gristhorpe and Scarborough, where it is from 5 to 10 feet in thickness.

It is a very shelly rock, and has yielded a large suite of species, for our knowledge of most of which we are indebted to Mr. Leckenby. These include Ammonites Herveyi, Pecten vagans, Lima duplicata, Modiola cuneata, Terebratula obovata, Rhynchonella concinna, &c.

The Cornbrash is used for road-mending, and for building walls, and is sometimes burnt for lime.

As the name implies, the soil in the South-West of England is well suited to the growth of corn; according to Prof. Buckman it contains more phosphate of lime than the subordinate Oolitic formations.

MIDDLE OOLITIC.

OXFORD CLAY.

CLUNCH CLAY AND SHALE. (Wm. Smith.)

The Oxford clay consists of dark-blue, yellowish or slatecoloured clay and bituminous shale. It effervesces with hydrochloric acid. It contains much iron-pyrites and selenite, and many septaria called turtle stones.'

Near its base is a bed of irregular calcareous sandstone of a concretionary nature and very fossiliferous, called the Kellaways (or Kelloway) Rock, by Smith, from Kellaways Bridge, near Chippenham, in Wiltshire. Although the clay derives its name from the county of Oxford, the Kellaways rock is not known in it.

The thickness of the clay varies from 300 to 600 feet; that of the Kellaways Rock is usually 8 or 10 feet in the South-west of England, and as much as 90 feet in Yorkshire.

Amongst the fossils are Gryphaa dilatata, G. bilobata,* Modiola bipartita, Avicula inæquivalvis,* Trigonia clavellata, Nucula nuda, Belemnites hastatus, B. Oweni,* Ammonites Jason, A. cordatus, A. excavatus, A. vertebralis, A. Calloviensis, and Ancyloceras Calloviensis.*

*

These belong to the Kellaways Rock.

Christian Malford, in Wiltshire, is a well-known locality for fossils of the Kellaways Rock.

Fossil wood has been found near Peterborough. Remains of Ichthyosaurus, Plesiosaurus, and Pleiosaurus, and of fishes, such as Leptolepis, and leaves of Zamia, are met with occasionally.

The Oxford Clay occurs near Weymouth, and extends across the Vale of Blackmore by Chippenham through Oxfordshire (350 feet) into Huntingdonshire.

Small hard nodules, called Kidney-stones, composed of reddish-brown clay with veins of Calc-spar, are frequently found in the Oxford Clay in the cliffs on the north shore of Weymouth.

In Northamptonshire the Kellaways Rock is represented by sands, sandstones, and clays. The clays are worked for brick-making at Oundle and other places.

The Oxford Clay forms the substratum of the western portion of the Cambridgeshire fens and those which border on Huntingdonshire; hence it has sometimes been called the Fen

Clay.

The researches of Professors Sedgwick and Seeley have shown that at Elsworth, near St. Ives, dark-blue iron-shot limestone about fourteen feet in thickness occurs near the top of the Oxford Clay (see p. 199).

At St. Ives a somewhat similar rock occurs at a lower level. Near Bluntisham a rock resembling these is found; and at St. Neots rubbly rock occurs, which may be on the horizon of the Kellaways Rock.

The Oxford Clay has been reached in the Sub-Wealden boring, near Battle, at a depth of over 950 feet.

The Kellaways Rock is very remarkable on account of its occurrence over a great extent of country, although at the same time it is not a persistent stratum: it is not known in Somersetshire or Dorsetshire. It is found near Welling

borough, Hackness, and Scarborough, and is sometimes known as the Hackness rock. In this district it contains clayey sandstone and ironstone, and the Killing Pits in Goathland Beck are considered to be the remains of rude mining operations in the beds. In Yorkshire the Oxford Clay (grey shale) attains a thickness of 150 feet.

The Oxford Clay is difficult and expensive to cultivate; it is mostly under permanent pasture. The old Forest of Braydon (Wilts) was situated on the Oxford Clay.

Septaria have been polished as marble at Weymouth, Melbury, and other places in Dorsetshire, where they are locally termed 'pudding-stone.'

The Clay has been largely worked for brick and tilemaking near Peterborough, and other places.

Beds of bituminous shale and lignite have led to futile searches for Coal in many tracts where the Oxford Clay is exposed.

The Kellaways Rock is used for building purposes in some places, also for road-mending.

The Oxford Clay is a retentive formation, and to obtain well-water it is necessary to penetrate it. At Boston a well was sunk 478 feet in it and abandoned.

CORAL RAG.

The Coral Rag where most fully developed is divided into :

Upper Calcareous Grit,

Coral Rag,

Lower Calcareous Grit.

In some localities the entire series is absent, or almost so, as in the Fen district, and as proved by the Sub-Wealden exploration in Sussex. This absence, which causes the Kime