# Transactions of the Geological Society, 1st series, vol. 4/On the Strata in the Neighbourhood of Bristol

VIII. On the Strata in the Neighbourhood of Bristol.
By RICHARD BRIGHT, M.D
member of the geological society.
[Read 15th November, 1811.]
With Notes extracted from the communication of
GEORGE CUMBERLAND, Esq.
honorary member of the geological society.
An elevated ridge of land divides the vale of Bristol from the plain which is watered by the Severn. The parallel strata which compose this ridge rise towards the north-west at an angle of about 45° emerging from beneath the horizontal beds upon which the lower part of Bristol is built, and are afterwards broken off as they come in succession to the surface. At the base of the western escarpment of this ridge the lowest of the highly inclined strata abut with their broken edges against the horizontal beds of another formation, which there occupy the plain forming low hillocks almost to the Severn. The Avon passing through a precipitous ravine cuts all these strata almost at right angles to their planes, and exposes a section of them which may easily be observed, and has supplied me with the principal materials for the present paper.
In the channel of the New River at Bristol a stratified red and yellow sandstone may be observed in strata nearly horizontal, but a little inclined to the north-west. The thickest of these strata are ​singularly divided into regular cubical or rhomboidal concretions, the planes of which cut the planes of stratification at angles of about 45°. Some parts of this rock make a fine building stone, as may be seen in the docks, where the stonework is constructed of it. There is a number of small cavities in the sandstone filled with crystals of sulphate of strontian of a red or dull white colour, both colours appearing sometimes in the same crystal.
in the low ground, on which great part of Bristol is built, hollows occur in the surface of the sandstone, which are filled with alluvial matter, such as clay, peat, &c. The clay is of a blue colour, and from 10 to 20 feet thick. On digging the channel of the New River 12 or 14 feet below the surface, a bed of peat was found more than 2 feet thick. At the top of the peat were a number of oak trees, tolerably sound, all lying towards the north.
On rising from the vale of the Avon to the higher part of Bristol a siliceous iron-stone appears. Great part of Clifton is built upon this rock, which is also found in the country south of the Avon, forming that part of the hill above Ashton on which Sir H. Smith's house stands, and passing a little to the south-east of Belmont. It is in the cavities and veins of this rock that the beautiful quartz crystals, called Bristol stone, are found. They form 6-sided ​pyramids; some are of the highest lustre and transparency, others variously coloured by iron ore, or containing acicular crystals of that substance, or of manganese; some are said to be pierced with needles of sulphate of strontian.
Behind Brandon Hill there are beds of sand highly impregnated with iron, and containing impressions both of shells and vegetables. In the descent on the south of Brandon Hill some singular masses of breccia project from the ground, containing rich iron ore, and assuming nearly a cubical form. The siliceous iron-stone of Brandon Hill has been found to make the best grinding stone for enamel colours. Below the siliceous iron-stone, upon the banks of the river near the Hot-well House, three small beds of coal make their appearance. These have been worked close to the river on its southern bank: and on the northern at the distance of two miles, near the Fort, a trial for coal was made some years since, but the seams found were not worth working.
Upon the banks of the Avon, immediately below the coal, there is found an extensive series of beds consisting principally of limestone, which form that high ridge of land which has been already noticed. This ridge passes on the north to Almonsbury and Alveston, and on the south to Clevedon, where the coal field of Nailsea begins. These beds upon the banks of the Avon are remarkably regular in their stratification, being all nearly parallel to one another and dipping to the north-west at an angle of about 45°. They are better observed on the northern than on the opposite bank, being on the former very much exposed by the operations of the quarrier.
Upon the top of this ridge and upon the fractured edges of the limestone strata, behind Clifton, there has been a partial deposition ​of stratified yellow sandstone, forming what has been called an upfilling. In the fissures of this rock crystals of carbonate of lime are found, and crystals of sulphate of strontian, which often assume a radiated form. This sandstone, having sometimes the appearance of a breccia extends to Redland. It is probably spread over the surface of the siliceous iron-stone already described; and in such a position it seems to have been found on Kingsdown in digging the vaults of Portland Chapel. The sandstone was there less firmly agglutinated, and the sulphate of strontian occurred about 4 feet below the surface in large irregular balls weighing many pounds. At Redland this sandstone and the strata upon which it rests are rather abruptly terminated, being covered by a limestone stratified horizontally in thin layers, containing ammonites, gryphites, and anomiæ in abundance, and agreeing in all its characters with the well known limestone called lyas. The lyas extends to Gotham, where some of the strata are remarkable for taking a beautiful polish, being known at Bristol by the name of the Cotham stone. This lyas burns to a brown lime which sets hard under water.
But to return to the limestone. I do not intend to describe in detail all the beds of it; but the following are what I thought best deserving of notice, from their commencement immediately below the coal down to the lowest in the series. The first part of the series is best observed on the northern bank of the river. ​
| 1. A mass of limestone composed almost entirely of organic remains, and containing much iron, with madrepores between the strata | 90 |
| 2. Ten thin beds of blue and close-grained limestone, with clay between them, in which madrepores are imbedded | 8 |
| 3. Limestone composed entirely of particles bearing marks of organization | 18 |
| 4. A very thin stratum of red clay, covering |
| 5.A layer of coaly matter, one inch thick. ​ |
| 6. Blue clay divided by bands of yellow clay | 12 |
| 7. Limestone resembling No. 3, this occurs at the distance of about 100 yards west of the Well house. |
| 8. Limestone that is quarried as being it for burning, forming magnificent cliff's about $\scriptstyle {\frac {1}{4}}$ mile beyond the Hot-well house. ​ |
| 9. Limestone in thin strata, impregnated with ochre so as to be unfit for burning. |
| 10. Ferruginous marl, containing a great many madrepores and shells quite detached from the rock. |
| 11. The first quarry of limestone. |
| 12. The second quarry of limestone. In the limestone of these two quarries the strata although separated by no intervening substance are very perceptible, preserving an uniform direction. |
| 13. Several thin beds of limestone which are not worked. |
| 14. At the distance of three or four hundred yards from No. 12, the assemblage of strata begins, which forms what is called the Black rock, so called from the dark colour of the stone. A third quarry is worked here. This rock is less tinged with ochreous infiltrations than the test usually are: it contains a great many shells and entrochi, and in its cavities are found dog's-tooth spar, cubes of purple fluor, acicular crystals of sulphate of strontian, and of oxide of iron. Similar cavities occur in the rock of the preceding quarry. |
| 15. Many thin beds of limestone divided by clay, some being very full of shells and entrochi, and others having scarcely any traces of organic matter. Some of these strata from the number of shells they contain may be recognised again on the rising ground at the foot of Leigh Down near the village of Leigh, on the southern side of the Avon. ​ |
| 16. A thin bed of limestone breccia containing rounded pebbles, and organized substances resembling the palates of fish. This bed has not been traced on the southern bank. |
| 17. Limestone highly crystallized, containing much iron, and composed in a great measure of organic matter. It is seen very distinctly on the northern bank of the river cropping out amongst the wood, and resembling a wall about 8 feet high. |
The limestone of St. Vincent's rocks when calcined yields a very pure lime: large quantities of it are exported for the use of the sugar works in the West Indies, in an unslaked state and packed in tight casks, and it is used extensively for building. All the roads in the neighbourhood of Bristol are repaired with the limestone, as are those in the neighbourhood of Gloucester, whither it is conveyed by means of the Severn.
Calamine is the most important mineral in point of frequency and value that the limestone yields. It is found in veins of calcareous spar crossing the limestone, accompanied by heavy spar and frequently by galena. The calamine is either amorphous or assumes the form of calcareous crystals which have been encased by it and since removed. The calcareous crystals in these veins have generally the dog's-tooth form; the heavy spar is not crystallized, but appears fibrous or composed of thin laminæ lying above one another. The galena sometimes presents very regular cubes, the angles of which are generally truncated. The calamine has hitherto been worked in a very imperfect manner: the vein is broken into, when it meets the surface; a rough windlass is placed over the hole, and a bucket is attached to a few fathoms of rope; two or three men work at the vein as long as the ore is found in abundance, or until the water impedes their progress. The mine is then deserted, but ​the heaps of rubbish at the mouth of the pit are often so rich in ore that considerable sums are paid for the privilege of washing them.
Manganese is also found in this district: it has not however been worked to any extent. The principal pit from which it is taken is in the parish of Ashton on the slope of the hill overlooking the valley to the west of the church. It is found in an iron-stone vein crossing the limestone. What little is found is used at the glasshouses and potteries of Bristol, and at the bleach yards in the neighbourhood.
To the limestone succeed other beds, in which a red siliceous sand is the prevailing ingredient. They lie in very regular strata from a foot to two inches thick, and parallel to those of the limestone. They are best observed on the southern bank of the river along the towing path for the distance of about half a mile from where the limestone terminates. These beds extend on the south of the Avon to Leigh, Failand and Charlton, and on the north they pass near to Sneed park towards Westbury. Some of the beds of this formation near to Abbots Leigh make a fine stone for building.
Among the uppermost of these beds are several composed of sandstone, the fissures of which are coated by calc-sinter, then a thin stratum of sandstone with evident marks of vegetable remains; below which is a red slaty sandstone very micaceous, and then a bed of siliceous pudding stone about 12 feet thick containing in some parts a number of white quartz pebbles.
About the middle of this series of sandstones there is found a singular stratum about 3 feet thick, composed of irregular balls of limestone packed closely together, the intervals being filled with fine sand. Below this the red slaty micaceous sandstone is repeated and at length disappears, being the last of the highly inclined strata that can be distinguished. ​
The last of these highly inclined strata at the base of their western escarpment are generally covered by beds of a very different character, which lie in horizontal layers upon the broken basset edges of the lowest beds of sandstone. This arrangement of the two formations may be observed to the south of the Avon on the towing-path just where the beds of sandstone terminate, and to the north of the river near to Sneed Park; at these places the sandstone is covered by horizontal beds, of that kind of breccia which I shall presently describe. These horizontal beds form a series of low hillocks extending from where the sandstone terminates to within two miles of the Severn. They are best observed on the southern bank of the Avon, at Hung-road near to Crokerne Pill, where their section is exposed at low tide in a perpendicular cliff nearly 60 feet high. The beds consist of a red loamy earth and of breccia arranged in the following order.
| Breccia | 3 or 4 feet |
| Red loamy earth, about | 30 |
| Breccia extending to the base of the cliff, and quite below low water mark. ||
The upper and lower beds of breccia present nearly the same characters. They both consist of calcareous and siliceous fragments cemented together by a calcareous base, having cavities in it, which are filled with calcareous and siliceous crystals, and sometimes with sulphate of strontian. The calcareous crystals have either the form of the primitive rhomb, or of the dog's-tooth spar, and are sometimes covered over with an incrustation of smaller crystals of carbonate of lime. The quartz is crystallized in six-sided pyramids. Besides the sulphate of strontian which is found crystallized in the cavities in small quantity, it occurs in large masses either imbedded in the breccia, or lying between the two beds of it. It occurs in blocks of ​many cwts. in the fields between Ham Green and Leigh, and I am inclined to believe that these are derived from the red loam which lies between the two beds, for I found a mass of it in a ditch lately dug on the slope of the hill below the basset of the upper breccia; but the circumstances were not altogether decisive. The sulphate of strontian from this place is seldom found well crystallized, the best of the crystals that I have met with being tables not exceeding$\scriptstyle {\frac {1}{4}}$th of an inch in length. The entire masses are generally snow white, having the appearance of a coarse grained loaf-sugar, but sometimes they acquire a reddish hue from a small quantity of ochre.
Small veins of galena are found in the breccia. The breccia is found near to Abbot's Leigh, from whence it extends in a position almost horizontal to Crokerne; and it probably occupies the whole space included by a line drawn from Leigh through Failand, Charlton, Portbury and Portishead, and thence returning again through Crokerne to Leigh. On the opposite side of the river it forms the stratum beneath Shirhampton, and runs up the valley below King's Weston hill, extending to the cast as far as Sneed Park. In some parts it is found at so high an elevation as to lead to a belief that there may be more than two beds of the breccia: in whatever situation however it is met with its general characters are the same.
The red loamy earth at Hung-road is traversed by veins of fibrous carbonate of lime, which are about an inch thick, and contains hollow calcareous nodules which are often lined on their inner surfaces with beautiful calcareous and siliceous crystals. The quartz varies but little in form; it is almost always in very short six-sided prisms terminated by two six-sided pyramids. It sometimes contains acicular crystals of iron ore: is generally transparent and colourless, but sometimes assumes an amethystine tint. The calcareous crystals vary very much in form, sometimes exhibiting that of the primitive ​rhomb, sometimes that of the dog's-tooth, and sometimes very complicated figures with numerous truncations. The whole cavity of the nodule is generally lined with small crystals, which are highly phosphorescent when thrown on an iron plate heated almost to redness.
On cutting through the loam there is generally found a bed of ochreous iron-stone about 1$\scriptstyle {\frac {1}{2}}$ foot thick. It is not known to what distance this bed of loam extends. The nodules have as yet been found chiefly in Hung-road wood, and some varying a little in appearance are seen on the opposite side of the river.
To the west of Crokeme Pill you find only a low alluvial plain, scarcely raised above high-water mark, and this continues on both sides of the Avon until it falls into the Severn.
With regard to the springs in the district I have been describing, it may be observed that those in the limestone are low and situated in the ravines, breaking out in many cases between high and low water mark. The hot spring at the Wells rises in the limestone 26 feet below high water mark, and 10 feet above low water, and no water is found at Clifton until the wells are sunk nearly to that depth. When you come to the sand-ridge upon which Leigh is situated, the springs are always found to rise in a high level, and they afford a good supply of water. In the horizontal strata to the west of Leigh very good water is obtained by sinking to the second or thick bed of breccia, or at the utmost by sinking a few feet into the stratum. There is a little spring in Hung-road wood which though perfectly clear has the property of covering every thing over which it flows with a brown calcareous crust. The quantity of water is small, and in summer the stream is frequently dried up.
As to the nature of the soil, the valley of Bristol and Ashton is as verdant an extent of pasture land as any in the kingdom. Its rich ​green colour is contrasted with the dark foliage of the elm, which is the prevailing tree of the county, very few oaks of considerable size being now found.
The limestone district has as yet produced little but heath and fern, the rock in general approaching too near the surface to be favourable to vegetation. Much of it however has been lately enclosed on the southern side of the river, and a part of that is of good promise. Within the limits of the sandstone and of the breccia there is very fertile grazing land.
* ↑ George Cumberland, Esq. of Bristol, has observed the same concretions, of which he has presented to the Society a drawing. According to Mr. Cumberland the sandstone alternates in its lower part with layers of a blue or greenish colour, and abounds with sulphate of strontian, the masses of which contain in their cavities crystals of the same substance of a lauceolate form and of an opake white colour. The masses are very fragile, and fall to pieces on attempting to disengage the crystals by the hammer. Sulphate of barytes is also found in the sandstone, but in small quantity.
* ↑ In the alluvial matter the horns and teeth of deer, the grinders of the boar, and nuts have been discovered. Blue phosphate of iron has also been found imbedded in a brown clay. The trees, according to Mr. Cumberland, had all fallen towards the south-west. Water worn pebbles and rounded blue flints were found at the bottom of the Canal near to the dam.
* ↑ Mr. Cumberland mentions the anomia producta as found in the sandstone which lies above the limestone.
* ↑ A beautifully crystallized specimen from these excavations was presented to the Society by Mr. Cumberland. It was found together with many other masses of the same substance imbedded in yellow marl. On digging the excavation for some houses at Clifton, according to Mr. Cumberland, the following minerals were found, but it is not known in what bed the vein occurred to which they belonged. Crystals of galena with foliated sulphate of strontian upon a matrix of sulphate of barytes. Quartz crystals enveloping needles of sulphate of strontian. These excavations are now closed, and the ground being built upon the minerals can no longer be procured.
* ↑ The following more detailed section of the beds lying above the coal marked No. 5, in the text, has been communicated to the Society by G. Cumberland, Esq. 1.—Sparry limestone, the edges of which being tinged with iron resemble lepidolite ft. 10 In. 2.—Red, blue and white schistose clay 26 3.—A stratum very full of fissures, the laminæ composed of quartzose sand united by a quartzose cement 9 4.—A stratum of what is called “ Dun marle,” containing very angular fragments of limestone and ironstone: the marl is red, blue and white, and is speckled with ferruginous sand and pieces of schistose clay 6 5.—A very hard mixture of ironstone and quartzose sand with portions of an oolitic texture 9 6.—A ruddy and arenaceous limestone, ochreous, passing into ironstone of a tine grain 2 7.—A stratum of ironstone I inch thick; then a very hard and line grained arenaceous stratum 6 1 8.—A line grained arenaceous stratum 2 6 9.—A stratum containing fragments of shells 4 10.—A stratum containing fragments of shells and corals, in part argillaceous, and having the oolitic texture; of a brown colour 4 11.—Three inches of ochreous clay with blue schistose clay, with oblong geodes of red iron ore very compact and hard 3 12.—Limestone having throughout the oolitic texture 12 13.—Schistose clay or stone with nodules of coral 5 14.—Very arenaceous limestone with oolitic texture. 1 15.—Schistose wet clay coloured by iron with nodules 2 16.—Limestone, somewhat oolitic, tinged with iron, containing broken shells. 4 17.—Dove-coloured, oolitic limestone with broken shells. The strata cracked. 8 3 18.—Grey compact limestone, irregularly oolitic 6 19.—A stratum somewhat arenaceous, tinged with iron 2 6 ─── 20.—A schistose limestone 1 21.—Two layers of soft limestone tinged with iron, separated by a layer of schistose clay 2 inches thick 22.—Dark and fine grained limestone, divided in part by loose schistose clay 2 23.—Seven thin layers of schistose limes tone, separated by loose friable schistose clay with nodules, the whole containing many shells of the winged anomias and the anomia producta, with coralloids 3 24.—Light coloured and fine grained limestone without animal remains, in texture resembling No. 22 1 25.—Limestone with small broken encrinites 2 26.—Dark oolitic limestone with broken shells 2 27.—Limestone with broken shells throughout 1 28.—Schistose clay 3 29.—Fine siliceous rock without shells 1 6 30.—Rock with oolitic structure partially coloured by blue clay 2 3 31.—A reddish limestone with small arms of the encrinite, their cavities filled with ochreous matter 6 32.—Coal about 2 inches thick, resting upon ironstone and red schistose clay, three or four inches thick. 6 Of these strata only two will burn into good lime, the rest being too arenaceous for the purpose. The organic structure observed in No. 3, of Mr. Bright's section is the oolitic texture noticed by Mr. Cumberland. Mr. Cumberland observes that although this texture I is still visible in the arenaceous rocks of a mixed nature, it disappears in those which are purely siliceous. He also mentions that an oolitic limestone may be observed lower in the series of the east side of the combe that separates the pure limestone from the black rock or swine-stone. The fossils of the black rock are the winged anomiæ, and rarely the anomia products, the palates of fishes, the claws of crustaceæ, corallines of various kinds, the mycetita of Woodward, the medusa encrinite, and millions of the stalks of encrinites, both round and oval. There has likewise been found in it a complete specimen of the head of an encrinus, and other heads of the encrinus have been observed imbedded in the limestone, and but little distorted. They were first noticed by Mr. Miller surrounding calcareous concretions in the black rock, which are penetrated with petroleum.Petroleum sometimes exudes from the rock in small quantity; it is very hot to the taste, and is used by the masons for an external application, assisted by friction, to remove rheumatic pains. The black rock is quarried for paving stones