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Comoseris, Cladophyllia, Thamnastrea, Isastrea, &c., and in greater numbers than in any other part of either of the adjoining strata. After a heavy rain the sides of the railway cutting afford a very interesting view of the fossil fauna of the period.

2 The Box Tunnel was chiefly formed through the Great Oolite and Fuller's Earth. An account of the works, written by a late member of our Society, in 1839, and published in a local journal of that date, contains some particulars which will be worthy of record in the Wiltshire Magazine. One of the greatest obstacles to the construction of the Great Western Railway was found to exist in Box Hill, a large extent of elevated ground lying directly between, and about equidistant from, Chippenham and Bath. This hill, the highest part of which is about 400 feet above the proposed level of the railroad, could not be avoided: to make an open cutting through it was impossible, and to perforate it was thought by many equally so. Nevertheless, Mr. Brunel, with that boldness for which he was so celebrated, adopted the latter plan, and accordingly it was determined that a tunnel, one mile and three quarters in length, 40 feet in height, and 30 feet in width, should be made through the hill. The extraordinary attempt of boring through this immense mass, consisting in great part of beds of solid freestone, was commenced in the summer of 1836 and completed in 1841. The difficulties that stood in the way of the performance of this great work, particularly that part of it on the east, were appalling; but they have been surmounted by the enterprise, skill and perseverance of Mr. Brewer of Rudloe, and Mr. Lewis of Bath, the gentlemen who contracted with the Directors for the completion of that portion of it. Independently of the difficulties arising from the laborious nature of the undertaking, the constant flow of water into the works from the numerous fissures in the rock, has been constantly most annoying; and in the rainy season so formidable as almost to destroy all hope of being able to contend with

In November, 1837, the steam-pump then employed being quite inadequate to the task of making head against it, the water increased so fearfully-having filled the tunnel and risen to the height of 56 feet in the shaft-as to cause the total suspension of the works till the July following. This would have caused many persons to have abandoned the work in despair; but Messrs. Brewer & Lewis, determined to fulfil their contract if possible, erected a second pump, worked by a steam-engine of 50-horse power, and had the satisfaction of vanquishing their enemy, and resuming their work. A few months afterwards (in November, 1838) the works were again stopped by an influx of water, which, however, was got under in ten days, the engine discharging 32,000 hogsheads of water in a day. In the portion of the tunnel between the seventh and eighth shafts (1520 feet in length), Messrs Brewer & Lewis commenced their operations at each end, working towards a centre; and when the two cuttings closely approximated, much anxiety was felt lest a straight line should not have been kept, and the union of the two portions of the work should not have been true. But, on breaking through the last intervening portion of rock, the accuracy of the headings was proved, and to the joy of the workmen, who took a lively interest in the result, and to the triumph of Messrs. Brewer & Lewis's scientific working, it was found that the junction was perfect to a hair as to the level, the entire roof forming an unvarying line; while laterally, the utmost

FOREST MARBLE.

All the strata between the white lime-stone and Cornbrash have been mapped as Forest marble, marked g; the white limestone forming a constant and easily recognized base upon which the variable strata of the Forest marble have been deposited. This formation includes shelly fissile oolite, in which false bedding is exceedingly prevalent, together with flagstones, sandy slates, clays, and siliceous sands.

On comparing the eastern portion of the district occupied by Forest marble with the western, it would appear that the fissile oolite of the one occupy the position of the clays and flags of the other. Thus, along the Great Western Railway, the fissile oolite rests on the white limestone, and is succeeded by bluish clays and limestones, shown in the cutting south of Kemble, while on the other hand, east of Cirencester, we find clays and flags resting on the white limestone, and succeeded by fissile oolite, upon which rests the Cornbrash. This will be apparent on comparing the position of the beds in the quarries at Amney with those shown in the Roman road three miles east of Cirencester. Thus we have the clays of one district occupying the position of oolite in another, and vice versâ.

Some of the bluish flagstones of the Forest marble present a curious collection of fragmentary fossils, in which we find shells

deviation from a straight line, was only one inch and a quarter! This in a cutting of 1520 feet in length, begun at opposite ends, and worked towards a common centre, is perhaps unexampled in the annals of tunneling. Notwithstanding the unfortunate accidents with which Messrs. Brewer & Lewis had to contend, the obstacles which crossed their path only incited them to greater efforts to complete their undertaking, and in order to make up for the delay occasioned by the irruption of water they employed upwards of 300 workmen. The cutting, on the Corsham side, extends through one solid bed of freestone or superior Oolite, in many places 130 feet thick. and lying upon a bed of fuller's earth, or clay, 120 feet in thickness; under which blue marl, resting upon lias clay is found. So uninterrupted and compact is the rock through which this end of the tunnel passes, that no masonry was required in any part of it, the stone itself forming sides and roof, and nothing being required at the bottom but the rails on which the carriages run. One ton of gunpowder was used every week in blasting this stone, and thirty-five tons of coal were also used in the same time.

of Mollusca, plates and spines of Echini, stems of Pentacrini, and fragments of plants strewn over the surface of the slab. Strata of this kind will be found in the quarries at Bicker's Barn and West Yatton near Corsham, the Folly north of Tetbury, in the quarries around Shipton Moyne, at Dudley House near Amney, and in quarries at Barnsley. The finest sections of this formation are exhibited in the railway cuttings at Corsham and Kemble.

In the neighbourhood of Tetbury and Cirencester, we find beds of yellow siliceous sand, containing large blocks of chert, a hard siliceous limestone which, on being split, seldom shows the concretionary structure. These masses may be seen in a quarry near Sandy Lane, south of Cirencester, of which the following is a sketch.

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Forest Marble near Cirencester.

a Slaty, false-bedded oolite, with oysters.
b Soft yellow sands, with large blocks of chert.

This bed of sand occurs also at Chavenage Green, north of Beverstone, and at Hillsome near Tetbury. The entire thickness of the Forest marble around Tetbury is about 60 feet, which becomes diminished to more than one half towards the north-east extremity of the district.1

1 The Forest Marble is well developed at Atworth, near Melksham. It is here worked for tile, stone and rough walling purposes. It contains many fossils, and the palates of Acrodus and other fish, (called by the quarrymen leeches,) are abundant. Near the residence of Sir John Awdry, at Notton, are several quarries of Forest Marble. Some of these contain beds of sharp siliceous sand, and exhibit very interesting examples of false bedding, and of the remarkable way in which these shifting beds of sand were borne about by the waves and tides during the deposition of the stratum. The railway sections in this neighbourhood are also very interesting.

FOSSILS FORM THE GREAT OOLITE AND FOREST MARBLE, 97, 98.

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Unicardium impressum. Lyc. & Mor. Cardium pes.-bovis. D'Arch.

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Mytilus sublevis. Sow.

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To these may be added several species from the catalogue of Bradford Clay Fossils, by Mr. Cunnington, in vol. vi. of the Wiltshire Magazine, p. 10.

For engravings and descriptions of the Mollusca of the Great Oolite, see Palæontographical Society's Publications, vols. for the years 1850, 1853, 1855 1861, by Messrs. Lycett & Morris; also contributions by Mr. Witchell and others, to Proceedings of the Coteswold Club.

+ An elaborate and very valuable contribution to the Geology of Wiltshire, is contained in a paper by Professor JAMES BUCKMAN, F.G.S., F.L.S., F.S.A., "On the Oolitic Rocks of Gloucestershire and North Wilts," read before the GEOLOGICAL SOCIETY, June 17th, 1857, and printed in the Journal of that Society, vol. xiv., p. 98. It is illustrated by a very accurate section of the country from Birdlip to Swindon, and from Blunsdon to Wanborough Hill, by Professor ARMSTRONG, C.E., besides other sections, tables of analysis, and lists of fossils.

Thus the northern portion of the county has been well explored by some of the best geologists. Of the middle and southern districts, though surveyed by the Ordnance officers, little has been published.

2 D

VOL. XI.-NO. XXXIII.

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