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THE ANALYST.

MEMOIR ON THE GEOLOGY OF THE VALE OF
EVESHAM.

(Read before the Worcestershire Natural History Society, March 13, 1834.)

Ar the request of several members of the Society, I have been induced to draw up an account of the geology of that part of the county of Worcester with which from personal residence I was best acquainted; an investigation which was the more desirable as this district does not appear to have been hitherto very minutely examined by the geologist.

Before I proceed to examine the subterranean structure of the Vale of Evesham, I will give a short sketch of its more obvious and superficial characters. This district is bounded on the E. by the lofty escarpment of the Cotteswold Range, and on the S. by Dumbleton and Bredon Hills, which constitute outliers of the same geological structure as the Cotteswolds, with which they have doubtless at some period been continuous. To the N. and W. this district has no natural boundaries, and might without impropriety be extended over nearly all Worcestershire, which is in fact one vast vale, of which the S. E. angle is denominated the Vale of Evesham.

The Vale of Evesham has an undulating surface, and, in some parts of it, hills occur of considerable steepness, and from 200 to 300 feet in height. These hills, however, by no means render the term vale inapplicable to the district, since from the lofty heights of Broadway and Bredon those minor elevations are barely distinguishable from the plain. From its low and sheltered position the average temperature of the district is high, and hence in a great measure, arises the fertility for which it has been perhaps too highly celebrated. In some parts of the district, indeed, tracts of very good land occur. This is chiefly the case where the surface consists of red marl, diluvial sand, or the alluvial deposits of the Avon. But where the lias clays come to the surface without any foreign admixture, as is the case over a large portion of the district we are considering, a wet tenacious soil is the result, requiring great labour and attention on the part of the farmer, and often rewarding him with very inferior crops. It would seem, indeed, that the lias is better suited for garden-ground than for agriculture. Near Evesham and Pershore are some extensive and valuable February, 1835.-VOL. II. NO. VII.

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market gardens, in which the lias clays, by a high degree of manuring and cultivation, are rendered very productive.

The whole drainage of the Vale of Evesham falls by a variety of small brooks and watercourses into the Avon. This river, though immortalized by the poets, has little to recommend it in the eyes of the painter. The clayey soil through which it flows imparts a considerable degree of muddiness to its waters at all seasons, and being kept by means of locks nearly on a level with the surrounding meadows, it loses all the picturesque effect which its neighbour the Severn derives from the steepness of its banks. From being kept constantly full, a moderate quantity of rain suffices to cause a rapid overflow, but as the water seldom remains on the land many hours before it subsides, it deposits but a small portion of the silt which it holds in suspension.

The Avon is commonly flanked on one or both sides by extensive meadows, whose level surface proves them to result from alluvial deposition. These meadows produce heavy crops of hay, which, from its excellent quality, bears generally the highest price in the market.

The bed of the Avon is for the most part deep, with a muddy bottom, with a few exceptions where beds of gravel occur. Its ordinary depth is from 12 to 20 feet, and its breadth from 30 to 50 yards.

Having thus given a sketch of the external features of the Vale of Evesham, we will proceed to examine its internal structure. In so doing it will be most convenient to begin with the highest stratum in the district, and proceed in geological order to the lowest. We shall thus investigate in succession the following formations-inferior oolite, upper lias shale, marlestone, lower lias shale, and new red sandstone.

The Inferior Oolite occupies the brow of Ilmingdon and Broadway Hills, and extends thence with great regularity along the brow of the Cotteswolds, into Gloucestershire and Somersetshire. It also forms a cap on the summit of Meon Hill, and of that magnificent outlier Bredon Hill, where it rises gradually towards the W. and N. to the height of about 900 feet above the level of the sea, and may be conveniently examined near the summer-house, which forms a conspicuous landmark to the surrounding country. On Broadway Hill it reaches the height of 1,086 feet, and forms the surface of that elevated table-land. This hill, as well as the whole of the Cotteswold Range, has lately been very carefully surveyed by Mr. Lonsdale, Secretary to the Geological Society, to whose labours those may be referred who wish for further information respecting that district.

The Inferior Oolite is quarried at Bourton-on-the-Hill, and in many other places, as a building stone, for which it is well suited. In appearance it has so close a resemblance to the Great Oolite that in many cases it can only be identified by examining its geological position ;-the mineralogical characters of both formations being the same. It commonly consists of a yellowish limestone, in which the "ova" or small globular particles from which

it takes its name, are more or less numerous and regular in different specimens. On Bredon Hill, portions of this stone sometimes occur of a brick-red colour, owing probably to the presence of an oxyde of iron.

On Bredon Hill the Inferior Oolite appears at some period to have been much disturbed; in the various quarries its strata are seen greatly shattered, and dipping in all directions, often with a high angle of inclination. These dislocations are doubtless of great antiquity, as the present outline of the surface does not seem to be affected by them. The general dip of the Oolite of Bredon Hill is to the S., and hence it descends with a gradual inclination much lower down on that side than on the N., where it terminates suddenly in a bold escarpment.

In many parts of England this formation contains an abundance of fossils, but they seem to be comparatively rare in those portions of it which abut on the Vale of Evesham. There has, however, been no scarcity of animal life in the period of its deposit, for a great part of the Oolite is composed of fragments of shells and corals, but it is rare to find these remains in a sufficiently perfect state to fit them for cabinet specimens. The most numerous shells are those of the genus Terebratula.

These researches, which have been chiefly confined to Bredon Hill, have as yet produced only the following fossils : Ammonita 1 species; Terebratula 5; Trigonia 1; Pecten 2; Cidaris 1; Pentacrinus 1; Terebellaria 1; Flustra 1; Sarcinula 1. Nine genera, 14 species.

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The next succeeding formation is the Upper Lias Shale. traces of this formation in our district are so imperfect that in many places its existence is rather to be inferred from analogy than proved from ocular evidence. Nevertheless, as there are some places where it certainly exists, it would be improper to omit this stratum in our list, especially as in the North of England it assumes a very important character, both in a geological and commercial point of view. In this and the adjoining counties, the stratum is vastly reduced in thickness, and there are no inducements for the speculator to penetrate its interior, and hence illustrative sections of it are rarely to be met with. Mr. Lonsdale states that he has met with it in many parts of Gloucestershire, and on his authority I have coloured it in the Society's Map, along the side of Broadway and Ilmingdon Hills, where it may be looked for at about three quarters of the way up. It occupies a similar situation in Bredon Hill, and may be traced round the N. side from the height above Aston-under-Hill to Wooller's Hill, its situation being commonly marked by a grassy slope, below the steep brow caused by the Inferior Oolite, and above the line of the Marlestone quarries. Numerous springs are thrown out along the line of its course, as is always the case where clay interstratifies with more porous strata.

This formation being in this district much concealed by grass and vegetable soil, but few fossils have as yet been found in it, but

if any good sections of it should occur, it may be expected to reward the geologist amply for the trouble of an examination.*

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The next stratum in the descending order is the Marlestone. This formation consists of a series of beds of sandstone, marl, and sand, in various degrees of induration. It may be traced along the side of the Broadway Range, at about half the height up; and skirts Bredon Hill in the same manner, where it forms the summit of five or six flat-topped projections, half the height of the main range, and jutting out from it on the N. and E. sides. In Dumbleton Hill, which is of inferior height, it occupies the summit, proving, by the regularity of its occurrence in these hills, that the intervening vallies have been denuded, and that Dumbleton and Bredon Hills are correctly termed outliers.

The Marlestone rarely possesses sufficient solidity of texture to qualify it for a building-stone, but in lieu of better materials it is quarried in many places to repair the roads. The Marlestone

of our district seems unquestionably to be the equivalent of the bed of the same name on the Yorkshire coast, which separates the Upper and Lower Lias Shales. In both localities it contains an abundance of fossils, including several species which are common both to Worcestershire and Yorkshire. In this neighbourhood the most numerous and remarkable fossils are, Belemnites, Gryphæa Gigantea, and Pecten Æquivalvis. The following is a list of the fossils hitherto noticed in it, and probably many more might be added on a closer examination of the several quarries where it is exposed.

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Ammonita 5 species; Nautilus 1; Belemnita 1; Terebra 1 Turbo 1; Trochus 1; Mya 1; Lutraria 1; Unio? 3; Corbula ? 1; Tellina? 1; Astarte 1; Cardium 1; Modiola 1; Pinna 1; Avicula 1; Plagiostoma 4; Pecten 9; Ostrea 1; Gryphæa 1; Terebratula 8. Twenty-one genera; 45 species.

We now arrive at a formation more important both in thickness and superficial extent than any hitherto described-the Lower Lias Shale, commonly known by the simple name of Lias. This stratum occupies nearly the whole of the Vale of Evesham, and extends from 200 to 300 feet up the sides of Bredon and Broadway Hills. Its total thickness is probably upwards of 500 feet. At Bretforton it has been sunk into more than 300 feet, in quest of coal, without being perforated. This excavation was commenced three years ago by a sanguine speculator, in spite of the warning advice of geologists, and after a great sum expended, is at last given up as hopeless. All scientific geologists know that true coal is only to be found beneath the New Red Sandstone, and that to seek for it in the Lias which is above that formation can only end in disappointment. And such is the enormous thickness of the New Red Sandstone, (as shewn by Mrs. Brown's excavation, which will be noticed hereafter,) that it is scarcely less chimerical to seek for it there, except, indeed, in the very lowest beds of that formation. If by diffusing a knowledge of the general principles of

* An account of this stratum and its organic remains, will be found in Mr. Murchison's excellent little work on the Geology of Cheltenham, just published.

geology, the Worcestershire Natural History Society shall prevent future speculators from sinking their fortunes underground in places where they will never draw them up again, our infant Society will not be without its use.

The Lias Formation consists here, as elsewhere, of a series of black or blue shales, producing, by exposure to the atmosphere, a cold, stiff, clay soil. At the lower part of the formation, thin beds of limestone occur, from 2 to 8 or 10 inches thick, which produce excellent lime, but when used as a building-stone are apt to shiver with the frost. At Binton, near Bidford, and at Haselor, these beds are thin, smooth, and of fine quality, and are used for flooring

and other purposes. Experiments, partly successful, have been

made to apply the Haselor stone to lithography. It is well adapted for the lithographic ink, but is not suited for crayons.

The strata we have hitherto described are very regular and conformable in their arrangement with respect to each other, but the Lias presents us with an extensive fault or break in the strata, by which the Red Marl beneath is unexpectedly exposed on the surface. This fault has been traced from near Netherton on the S. to Lower Bentley on the N., a distance of 15 miles, and is distinguished on the map by a narrow strip of Red Marl running towards the S., with Lias on each side. From Netherton to Radford, on the Worcester and Alcester road, this fault is marked by a shallow valley, from half-a-mile to a mile in width, crossing the valley of the Avon, and interrupted near the middle of its length by the Cracombe Hills. Throughout this space the eastern side of the valley is the highest and steepest, the rise on the W. being very gradual. This valley is one of those which geologists term vallies of elevation, being a gap, caused by strata separating and sloping off to either side in consequence, as they suppose, of an elevation of the strata beneath. But as the same effect, (as far at least as relates to level,) would ensue from the depression of two neighbouring districts, as from the elevation of some point between them, it would perhaps be better to give to vallies of doubtful origin a name founded, not on theory, but on facts, and to term them anticlinal vallies, that is, vallies in which the strata on either side dip away in opposite directions.

The portion of Red Marl exposed by the fault in question, is at first a narrow strip, with a regular width, of about half-a-mile, commencing near Netherton, and passing between Cropthorne and Charlton, whence it spreads out to a mile in width, reaching from Cracombe nearly to Chadbury. The Cracombe Hills cause an interruption to the anticlinal valley, and the Lias, which is continued uninterruptedly along their summit, forms a kind of bridge, connecting the Lias on the two opposite sides of the line of fault. The Red Marl rises about three quarters of the height of these hills, and may be traced dipping beneath the Lias, both on the E. side and the West.

Beyond Cracombe Hill the valley resumes its course as far as Rouse Lench and Radford, with a width of half to three-quarters of a mile. The eastern limit of the Red Marl follows the brow of a

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