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of these two estuarine series, that of the Northampton Sand, we must imagine the beds as being carried down to great depths in the earth by the deposition upon them of the superincumbent strata. But at the same time another most important cause has come into operation, namely, the passage through some portions of the rock of subterranean water containing carbonate of iron in solution. By this agent carbonate of iron was deposited in the substance of the rock, while portions of the siliceous and other materials were dissolved; and these entering into new combinations, were in part re-deposited in the mass of the rock in the form of oolitic grains, and in part, probably, carried away in solution. During the existence of the beds under a great pressure of overlying rocks, they would likewise become consolidated and jointed. These metamorphic processes would probably take place with extreme slowness, and may possibly still be going on, where the rock remains deep-seated in the earth; by their means portions, greater or less, of the sandy strata, but always those resting immediately on the impervious Upper Lias Clay, would be gradually converted into solid and jointed rock beds, composed principally of carbonate of iron. The next stage in the course of alteration in these rocks would commence when, by the action of denudation, portions of them were brought again near to the surface, so as to be traversed by the atmospheric waters, entering them as rain and passing away from them as springs. The action of this water is to remove the carbonic acid and soluble salts, to change the protoxide of iron into hydrated peroxide, and to redistribute it in such a manner as to produce the remarkable cellular structure of the rock, and also the mammillated, botryoidal, and sculptured surfaces. Finally, by mechanical, as distinguished from chemical, subaërial denudation, the beds of Northamptonshire iron-ore nearest the surface are disintegrated and broken up, and the softer and less ferruginous portions to some extent carried away in suspension, and thus deposits, composed of the harder and denser materials, formed, constituting the bed usually worked as an iron-ore. (J. W. Judd.)
UNDER OOLITE. (Smith.)
The Inferior Oolite consists of buff-coloured sandy oolitic and iron-shot limestone, with occasional beds of compact limestone. It is generally darker in colour than the Great Oolite.
At Leckhampton Hill it admits of the following divisions:
6. Upper Ragstone) and Clypeus bed) 38 feet-Zone of Ammonites Par5. Lower Ragstone
4. Upper (flaggy) Freestone
3. Oolite Marl
2. Lower Freestone
1. Pea Grit
with C. Plotii.
The Pea-grit (according to Mr. Hull) is composed of flattened spheroidal masses about the size of a pea, and one fourth or one fifth of an inch in diameter. Many of the ovules consist of layers of carbonate of lime, aggregated around some organic or inorganic fragment: some appear to be small rolled fragments of limestone. This division is very fossiliferous.
The Lower Freestone yields the building-stone quarried at Bourton, Broadway, Guiting, Stanway Hill, Cleeve Cloud, Leckhampton Hill, Painswick Hill, Birdlip, Sheepscomb Hill, Hellcomb, Lyreford, Brockhampton, and Longborough.' The freestone is largely composed of comminuted shells. The Upper Freestone, also quarried, is oolitic. The fossils include Echinoderms, Nucleolites (Clypeus) sinuatus, Acrosalenia, Hemipedina; Molluscs, Gryphia Buckmani, Pholadomya fidicula, Trigonia costata, Ceromya concentrica, Ostrea Marshii, Myacites musculoides, Terebratula fimbria, T. globata, T. plicata, Rhynchonella tetrahedra, R. spi
Beds 5 and 6 have locally, in the Cotteswold Hills, been divided into paleontological zones by Mr. Lycett and Dr. Wright: thus in descending order they are represented by the Pholadomya Grit, the Trigonia Grit (T. costata), the Gryphite Grit (G. subloba), the Chemnitzia Grit (C. procera): all these have been collectively grouped as the Spinosa
1 The stone when first removed can usually be cut by the saw; it hardens upon exposure.
stage, characterized by Rhynchonella spinosa. No. 3 has been termed the Fimbria stage, being characterized by Terebratula fimbria.
The beds which rest on the Pea-grit are, according to Mr. Hull, frequently pierced by Lithodomus attenuatus: the upper bed of the Ragstone is also bored by Lithodomi.
Burton Bradstock is so well known as a locality for Inferior Oolite fossils, that it may be interesting to give the following section afforded by the quarries in the zone of Ammonites Parkinsoni which was taken at this locality by Dr. Wright:
5. Coarse ferruginous iron-shot oolite, containing many fossils: Ammonites Parkinsoni, A. Truellei, A. subradiatus, Ancyloceras annulatum, Astarte obliqua.
4. Thin-bedded oolitic limestone, with few fossils
3. Brachiopoda-bed; a rich shelly oolite, containing immense
numbers of Terebratula sphæroidalis
2. Thin-bedded oolitic limestone; few fossils
1. Coarse brown oolitic limestone
The quarries at Halfway House, between Sherborne and Yeovil, and those near Bradford Abbas, have yielded many fossils.
The two well-defined divisions of the Inferior Oolite of the south of England are thus described by Dr. Holl :—
Upper Ragstone, consisting of light-coloured, coarse-
In the neighbourhood of Bath the Inferior Oolite is about 60 feet in thickness.
Prof. Hull observes that this formation, which in the Cotteswold Hills attains a thickness of 264 feet, is represented in the neighbourhood of Woodstock by only 5 to 10
feet of the highest member of the series. At Sarsden the thickness is about 20 feet; at Fawler, near Stonesfield, 10 feet; at Enstone there is only a trace; and along the valley of the Cherwell it is altogether absent.
The Inferior Oolite forms good building-stone at Dundry Hill and to the south of the Mendips; the quarries at Doulting,' those near Yeovil and at Ham Hill are well known. At Ham Hill the stone is chiefly composed of comminuted shells. It has also been worked at Stinchcombe, Wotton Underedge, and other places in the Cotteswold Hills.
The soil is reddish-brown and brashy; the character of the ground is hilly, and sometimes barren, but where the soil is deep it is fertile.
Resting upon the Alum Shale (Upper Lias) of Yorkshire is the series known as 'Dogger.'
The Dogger is a sandy and oolitic ironstone, but the series is sometimes taken to include not only the Dogger proper, but the grey and yellow (Blue Wick) sands which underlie it.
The Upper Lias seems to pass gradually upwards into the beds above, which are classed as follows:
Yellow sandstone and ironstones (Dogger) including
Yellow sands and Sandstone, with Terebratula Bed (T.
20 to 25
Blue Wick Sands.
Grey sands and sandstones, containing a Serpula Bed,
20 to 25
Upper Lias (passage beds), Sandy shales yielding Ammonites striatulus
1 This stone was used in the construction of Wells Cathedral and Glastonbury Abbey.
2 It is not certain whether the Dogger (sometimes termed the Scar of