Bristol Coalfield Research Articles

The Igneous Rocks and Associated Sedimentary Beds of the Tortworth Inlier

I. Introduction The Silurian rocks of the Tortworth district in Southern Gloucestershire present several features of geological interest. Lying to the north of the horseshoe ridge of Carboniferous Limestone, which forms the rim of the Bristol Coalfield, they share in the synclinal disposition of the Palæozoic strata. They underlie the attenuated Old Red Sandstone, which in this district is not more than some 200 or 300 feet thick; but the exact relation of Silurian to Old Red is nowhere clearly seen. The strata include beds of Ludlow, of Wenlock, and of Upper Llandovery age, the last-named being originally regarded as Caradoc. The chief points of interest are: (1) the remarkable attenuation of the upper strata, the Ludlow Beds not exceeding 100 feet in thickness, and the Wenlock attaining a thickness of at most 700 feet, probably less; (2) the limited number of fossils recorded; and (3) the occurrence of igneous rocks interbedded with the Upper Llandovery strata, and passing up to, or perhaps just into, the Lower Wenlock Beds. It is with these igneous rocks and their relation to the sedimentary beds that this paper deals. The trap-rocks were carefully studied and described by Thomas Weaver in 1819. He regarded it as ‘evident that the trap constitutes discontinuous beds included in and parallel to the continuous series of the stratified transition-beds’; but, as a faithful disciple of Werner, he hastened to add that, since these stratified beds were ‘undeniably aqueous products, I do not perceive how we can avoid extending

XXVI.—On the Fossil Flora of the South Wales Coal Field, and the Relationship of its Strata to the Somerset and Bristol Coal Field

The Coal Measures of the South Wales Coal Field fall into three well-marked divisions:—I. The Upper Pennant or Upper Penllergare Series.II. The Lower Pennant Series.III. The White Ash Series.In 1885 I paid a visit to this Coal Field, with the object of studying its Fossil Flora, hoping by this means to ascertain the relative position of the Welsh Coal Measures to those of the other Coal Fields of Britain.

2. On the Fossil Flora of the Radstock Series of the Somerset and Bristol Coal Fields. (Upper Coal Measures.) Part I

2. On the Fossil Flora of the Radstock Series of the Somerset and Bristol Coal Fields. (Upper Coal Measures.) Part I

2. On the Fossil Flora of the Eadstock Series of the Somerset and Bristol Coal Fields. Concluding Part

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A Recently-Discovered Deposit of Celestine

IT may, perhaps, be worth mentioning that a large and valuable layer of celestine has been lately found at Yate, in Gloucestershire. It lies just below the sub-soil upon a bed of red Triassic marl, which rests unconformably upon the coal-measures, just at the eastern edge of the Bristol coal-field in that district.

Proceedings of the bristol naturalists' society. New series, vol. iii. part ii. (1880). 8vo. Pp. 83–174. Also, new series, vol. ii. (1877–8–9). Flora [recent] of the bristol coal-field. Edited by J. W. White. Part I. Thalamifloræ. 8vo, 40 pages. Bristol, 1881

<i>Proceedings of the bristol naturalists' society</i>. New series, vol. iii. part ii. (1880). 8vo. Pp. 83–174. Also, new series, vol. ii. (1877–8–9). <i>Flora</i> [<i>recent</i>] <i>of the bristol coal-field</i>. Edited by J. W. W<scp>hite</scp>. Part I. Thalamifloræ. 8vo, 40 pages. Bristol, 1881

The Price of the “Memoirs of the Geological Survey”

THE publication of Mr. Skertchley's “Manufacture of Gun Flints,” in the Memoirs of the Geological Survey, seems to be a good opportunity for again bringing under notice the absurd price charged for some of the Survey volumes. In NATURE, vol. xviii. p. 562, Prof. Boyd Dawkins drew attention to this subject, and urged the necessity of issuing the “Memoirs” at a reasonable price; but this last publication shows that the Stationery Office does not intend to mend its ways, but will still try and put the information it issues as far as possible out of the reach of the public. The fact I should like to draw attention to as regards the price of the “Memoirs” is the absurdity of the amount charged for some of the volumes, as proved by others issued by the Survey; and a glance at the facts seems to show that the prices are fixed without any regard to the size or quality of the book. Mr. Skertchley's pamphlet consists of 80 pp. and 71 figs., and this, in a paper wrapper, is priced 17s. 6d.! Now, take Prof. Judd's “Geology of Rutland,” this contains 320 pp. (or exactly four times as many as Mr. Skertchley's) 11 plates and 19 woodcuts, and the price of this, in cloth, is 12s. 6d., or 5s. less than the one of 80 pp. Another example is Mr. De Ranee's Memoir on the “Superficial Geology of the Coasts of Southwest Lancashire,” which consists of 139 pp., and 20 woodcuts, and for which we have to pay 17s.; compare with this Mr. Woodward's “East Somerset and Bristol Coalfield,” containing 271 pp., 9 plates, and 23 woodcuts, which is only one shilling more than the last-named, and is issued in cloth. But perhaps the most curious two to take together are Mr. Skertchley's volume on the “Fenland,” and Prof. Green's “Report on the Yorkshire Coalfield.” The former of these contains 335 pp., 24 plates, and 36 woodcuts, and is published at 2l., the latter has 823 pp., 26 plates, and 125 woodcuts, and yet the price is only 2l. 2s. It is certainly hard to understand why we should be charged 2l. for Mr. Skertchley's volume, if one the size of Prof. Green's can be produced for 2l. 2s. One would imagine that books issued with the public money would be sold as cheaply as possible; and it is to be hoped that some friend to Science in Parliament will ask a question of the Government, and see if it is absolutely necessary that these Memoirs should be published at such famine prices.

On the Triassic Rocks of Somerset and Devon

I ntroduction . T he Triassic areas of Devon and Somerset may be divided into three lithological districts:—the first, on the north and north-east of the Polden Hills; the second, on the north-east, east, and south-east of the Quantocks; the third, comprising the rest of the Triassic area, lies between Watchet and the south coast of Devon, being bounded on the west by the Devonian and Culmiferous highlands, and on the east by the Quantock and Blackdown ranges. The first of these districts is too well known to call for more than a general description in this place. In the Geological-Survey Memoir on the Bristol Coalfield it has been already treated of, the labours of Conybeare and Phillips, De la Beche, and the late Mr. Wm. Sanders, with those of Messrs. Moore and Etheridge having left little to be desired as far as the description of the Triassic strata is concerned. With reference to the last-mentioned districts, of which we purpose to give a more detailed though far from exhaustive description, it is different, the relations of the Trias not having been before established, except so far as might be inferred from a study of the splendid section along the coast between Seaton and Torquay. Sir Henry De la Beche, in his report upon the geology of Devon and Cornwall, gives a very general description of the Trias, without attempting a classification of its component marls, sands, and conglomerates, which the greater time occupied in the resurvey of the district has enabled me

V. On the Geological Structure of the District around Kingswood Hill, near Bristol; with especial reference to the supposed Development of Millstone-grit in that Neighbourhood

I have for some years had serious doubts as to the correctness of the Map of the Geological Survey so for as it relatesto the supposed presence of Millstone-grit in the northern portion of the Bristol Coal-field in the neighbourhood of Kingswood Hill; and in a foot-note to a most valuable lecture delivered by my friend Mr. Robert Etheridge, F.G.S. (of the RoyalSchool of Mines) at the Bristol Mining School in 1857, and published in a volume of Lectures issued by that Institution, Ihad, so long ago as that year, expressed doubts as to the existence of Millstone-grit at the surface near kingswood. Sincethen I have had much greater opportunities of investigating the matter, having taken, with my partners, a large tract of mineral property in that district; and the results of those investigations thoroughly confirm the doubts I had previously entertained, and in fact fully satisfy my mind that what is shown as Millstone-grit on the Government Geological Map, as also on the valuable map lately published by Mr. William Sanders, F.R.S., of Bristol, is really nothing more than one of thesandstones (the ‘Holmes Rock’) so common in the Coal-measures proper, and developed on a grand scale in the Pennant-grit dividing the Upper and Lower Coal-series of all the South-western Coal-fields.

The Practical Application of Geology in Coal-Seeking

The case now to be detailed is one which was investigated at Malmsbury, in Wiltshire. At this place the worthy burgesses to whom the land had been bequeathed by king Athelstan had undoubted evidence that a shaft had been sunk for coal on the land in question. This operation was actually performed about a century ago, and, in order to pay the attendant expenses, the whole of the timber from a large estate was felled and sold. Tradition said that “the coal had been arrived at, but, in reality, those engaged had been bought off by some proprietors in the Bristol coal-field, for fear the new district coal should come in competition with theirs.” But, besides evidence of this kind, about two pounds of Lignite was submitted to my inspection, with the assurance that it burnt like good coal; and the argument founded upon this pseudo-coal was as follows:—“This coal is about two inches thick at about 20 feet from the surface; how thick, therefore, may we not expect it at a hundred yards?” But for fear this should not be deemed conclusive, a bill of sale of some land in the district, many years before the date of this examination, was produced, on which was the statement that “Mining rights were reserved.” But I should state that upon inquiry it was found that the said land belonged to the Crown, and I believe that in all Crown lands there is a reservation made of mining rights; thus this, it will be perceived, was no evidence whatever of the presence of mineral matter. These, then, were the foundations upon which the burgesses relied; now for the geological examination.

XXXV.—Notice of the Discovery of a mass of Trap Rock in the Mountain Limestone of Bleadon Hill, in the County of Somerset.

I feel much pleasure in announcing to the Society, that a cutting for the Bristol and Exeter railway through the extreme western termination of Bleadon Hill has within these few days disclosed a mass of fine porphyritic trap, the first instance hitherto observed of the occurrence of an igneous rock in the Mendip Hills, or within the area of the Bristol coal-field. The trap varies from a granular greenstone with hornblende to a compact porphyritic rock, inclosing amygdaloidal kernels of calcareous spar and brown hematite; other specimens exhibit crystals of glassy felspar, and the rock is sometimes laminated and friable. The bed of mountain limestone which rests immediately on the trap differs in colour, and is much more brittle than the other strata. Rare as such igneous products are in this region, they are scarcely less so throughout the whole of Exmoor and the Quantocks; for, except the syenitic granite and trappean porphyry of Hestercomb in the Quantocks, first noticed by Mr. Horner*, a slaty porphyry I met with a little north of Simmons-birth in Exmoor, and the elvan blocks near Morte Point, mentioned by Mr. De la Beche†, all associated with the same slate series (No. 5. of my subdivision), which rests on the granite of Lundy Island, I know of none. The next nearest igneous rocks are those about Tortworth in Gloucestershire, in the Caradoc sandstone division of the Silurian system of Mr. Murchison. The cutting for the railway intersects the broadest part of the ridge of lias