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January 28, 1938
The Busty Seam
The Department of Scientific and Industrial Research has issued a physical and chemical survey of the national coal resources, No. 41,* dealing with the Busty seam in the Northumberland and Durham coal field. We make the following abstract:—
This report is considerably larger than others so far issued in the series, for, the seam usually occurring in two parts which it was expedient to sample separately, it is in effect a report on two seams. Further, the Busty seam is not only of very widespread occurrence and considerable importance throughout the Durham area of the coal field, but is recognised and has been examined in the Northumberland area also. This necessitated the taking of a larger number of samples than usual, the results being given of the detailed examination, from floor to roof, of samples from as many as 56 sampling localities. It is hoped that the comprehensive survey of a seam forming such a well-known horizon over so wide an area may serve as a datum, simplifying and reducing the work necessary on other seams in this field.
The coal measures of Northumberland and Durham occupy a triangular area of 900 sq. miles (including under-sea royalties), with its apex in the north near Alnwick and its base between Hartlepool in the south-east and Eggleston (near Middleton-in-Teesdale) in the south-west. Structurally, the field forms the western side of an irregular basin, elongated in a north and south direction, the eastern side of which is cut off by the sea. The seams outcrop on the west and south and some continue eastward beneath the North Sea. With the exception of a covering of Boulder Clay, the Coal Measures are exposed at the surface over the greater part of this area, being concealed beneath a cover of newer rocks in the south eastern corner only.
A great thickness of limestones, lying beneath the Coal Measures and separated from them by the Millstone Grit, occupies large areas of country to the north and west of the Coal Measure basin. These rocks are of a nature intermediate between those of Scotland, which contain valuable coals, and those of the south, which contain no coal. The seams in them, therefore, increase in number and value northwards and in Northumberland assume some economic value.
The Coal Measures consist of alternations of sandstone, shale, coal, and fireclay, and contain some 20 workable seams. The Brockwell seam is taken as the base of these productive measures and, although the top is nowhere present, they are from 1,400 to 1,800 ft. thick. Beneath, the Brockwell seam, in the so-called Ganister Measures, occur one or two thin but workable coals. The naming of the seams, and their correlation from area to area, is in a state of great confusion, the same seam often bearing different names in different places and, in some instances, different seams bearing the same name, even in the same pit shaft. Several important faults, with throws up to 1,000 ft., cross the coal field, chiefly in an east-west direction. Igneous dykes, having a similar trend, are present, and in some areas have locally "burnt" the coals, with a consequent loss of volatile matter and reduction to a cindery condition.
The reserves of coal in this field (excluding the Limestone Coals) were estimated by the Royal Commission of 1905 to amount to approximately 8,950 million tons. From that date to 1934, according to the statistics published in the annual reports of the Secretary for Mines, approximately 1,400 million tons of this coal were raised, leaving reserves of the order of 7,550 million tons.
The seams are all of a bituminous nature, but differ markedly in character to the north and south of the Tyne, those in Durham yielding some of the best coking and gas coals in the country, and those in Northumberland, steam and house coals of high quality. With previous reports it has been customary to treat Northumberland and Durham as separate areas, but the Busty seam (as the Stone Coal and Five-Quarter seam) is of considerable importance in south-west Northumberland, although over the remainder of the Northumberland area, it is only worked in isolated areas in which correlation is doubtful. A separate survey of the Northumberland area is not desirable at the present stage of development, and it seemed advisable to consider the coal field as a whole. This report, therefore, deals with the Busty seam of Northumberland and Durham.
Occurrence and Extent.
The Busty and its equivalents is a well-known horizon occurring between the Harvey (Beaumont or Towneley) and Brockwell seams over the greater part of the Northumberland and Durham coal field. It attains its maximum importance in west Durham, where it yields a soft coking coal of exceptional quality. In south Durham it produces a slightly harder coal which is used for coking, gas, steam and general purpose work.
In the vicinity of the outcrop in west Durham the reserves are generally small. They are greater to the east and in north Durham, to the west of the River Wear, there are some royalties with virgin coal and several other areas where the reserves exceed 60 per cent. In south Durham, over an area of approximately 40 square miles, the average reserves approach 80 per cent.
In east Durham the seam has not been generally proved, but in isolated districts where it is worked, it yields a good gas coal. In some localities it thins considerably and over a belt stretching from Durham almost to Sunderland the seam is probably too thin for future development. It seems possible, however, that it will become of commercial importance in limited coastal districts. In some localities of east Durham there is a possibility of incorrect correlation.
In south-west Northumberland the Busty seam produces a good coking coal. Near the River Tyne the reserves are very small, but increase to the north and east. Over the greater part of the Northumberland area the supposed Busty seam has only been developed in isolated royalties, but a study of the available information does not indicate that it will ever become more than a seam of minor importance.
In some districts the Busty exists as a single seam of 5 to 6 ft. in thickness containing one, and occasionally two, small bands of shale or clay. In other districts one or both of these bands develop to such an extent that the upper and lower sections are worked as separate seams. The main band, usually termed the Busty Band, is normally regarded as a characteristic feature of the seam. It is subject to rapid changes in thickness : thus it is not uncommon to find the Busty worked both as one thick seam and as two distinct seams in different parts of the same royalty.
During the course of the survey, data relative to the thickness of the Busty Band was collected from all possible points. The Busty Band is less than 3 ft. thick over a district from 4 to 6 miles wide, extending from Beamish to the neighbourhood of Browney Colliery, with the River Wear as an approximate eastern boundary. In the extreme south, also, the band is generally thin, although information in this district is scanty. In the Cornsay, Crook and Willington district of south-west Durham, the band is rarely less than 3 ft. thick and the Top and Bottom Busty seams are normally worked separately. In north-west Durham there are areas where the band is thin at Consett and Burnopfield, but north of the River Derwent it is consistently thick and the two sections are always considered as distinct seams. In east Durham insufficient evidence is available to enable any statement to be made. Over a part of the area where the seam is thin, washouts have been reported, and in some localities correlation is uncertain. In the Bowburn, and some other south Durham districts, the Busty Band, although not greater than 3 ft. in thickness, is composed of two parts of shale separated by a few inches of coal.
Nomenclature and Correlation.
The accepted nomenclature of the Busty seam, although changeable, is reasonably well known and recognised, the following showing the standard variations encountered in different districts :—
With regard to the confusion between the two Five Quarter seams in the Stella-Chopwell and the Prudhoe-Wylam districts, it may be noted that Buddle,** over a hundred years ago, referred to the Top Busty of Ryton and Walbottle as "Stone coal, Five Quarter or Main coal," and to the Bottom Busty as "Under Five Quarter, or Six Quarter." In addition, the Bottom Busty seam in the Benwell district was formerly termed the Denton Low Main and at East Walbottle the presumed Top Busty and Bottom Busty seams are known as Dinky and Brockwell respectively.
The correlation of the Busty seam is well established over the greater part of the Durham area, but some confusion exists in the east. Reference has already been made to the possibility that the Busty seam of the extreme south-east may be incorrectly named. A similar statement is also applicable to North-East Durham, where it is probable that the Brockwell seam of Usworth is correlative with the Busty seam of North-West Durham — a nomenclature similar to that of Usworth being adopted for the lower unworked seams in the north-east district. Much of this confusion may be attributed to the thinning of the Busty and Brockwell seams on the eastern side of the Durham area. Considerable doubt exists with regard to the Busty seam north of the River Blyth.
General Description of Seam.
Over the greater part of the Durham area the Busty seam consists mainly of soft, bright coal of good quality. From a measurement of the banded constituents it is estimated that the average durain content does not exceed 15 per cent., though there is a definite increase in the south, where the seam changes from a coking to a general-purpose coal.
In South-West Northumberland and part of North-West Durham, where the seams are termed Stone Coal and Five Quarter, the coal becomes stronger, but in very few instances are bands of actual dull coal observed, the durain being finely interbanded with clarain.
The bright coal of the Busty seam is, in general, exceptionally clean and in the western part of the Durham area it is estimated that it could, without difficulty, be cleaned to yield a product with ash and sulphur contents below 2.0 and 0.8 per cent, respectively. In many instances it was possible to separate from pillar samples subsections of bright coal which, without further treatment, yielded figures of this order.
With some pillar samples it was found difficult to estimate the durain content, and it was rare that a dull coal was obtained which could confidently be termed durain; frequently it was cleated and only dull by comparison with the bright clarain and vitrain which composed the greater part of the section. A sample of s.s. 2 from Locality 21 was sent to Mr. C. A. Seyler, of Swansea, for independent examination. In the description of this sample, s.s. 2 is "mainly bright coal, containing one or two small layers of duller coal which could not properly be described as durain-rather as dull clarain." Mr. Seyler states that "examination of the lithological constituents by naked-eye inspection left one in doubt as to whether certain bands were a dull clarain or a durain. . . . The section was divided into small pieces, each of which was polished and examined microscopically; doubtful cases were also examined by means of thin sections. ... I did not find anything which was undoubtedly durain."
Sampling and Analysis.
Approximately 170 samples of the Busty seams were taken from 58 localities. The majority of samples consisted of pillars of coal cut vertically from the face; where this is impracticable, a strip sample of approximately the same size as a normal pillar sample was taken, with due precautions against the inclusion of dirt and extraneous matter. The methods of analysis were those of the British Standards Institution. The laboratory carbonisation assays for samples from Localities 1 to 56 were carried out in the high-temperature modification of the Gray-King apparatus.
* H.M. Stationery Office. Price 6s. net.
** Buddle, J., "Synopsis of the Several Seams of Coal in the Newcastle District," Trans. Nat. Hist. Soc. Newcastle, 1830.
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