COAL FORMATION. 



COAL FORMATION. 



(Table continued) 



The following arrangement in tht of Megan. Conybeare and Phillips, 

 and from its simplicity will serve as a plan for some general remarks 

 on the coal-fields of Great Britain : 1. The great northern district, 

 including all the coal-fields north of the Trent. 2. The central 

 district, including Leicester, Warwick, Stafford, and Shropshire. 

 S. The western district, which may be subdivided into north-western, 

 including North Wale*; and south-western, including South Wales, 

 Gloucester, and Somersetshire. 



Coal- Dittrict North of the Trent. This great coal formation encircles 

 the whole Penine mountain chain on the east, south, and north ; not 

 however in one uninterrupted line, but in a series of detached coal-fields. 

 1. The Coal-Field of Northumberland and Durham. 2. Some small 

 detached Coal-Fields in the North of Yorkshire. 3. The Coal-Field of 

 South Yorkshire, Nottingham, and Derby. 4. The Coal-Field of 

 North Stafford. 5. The South Lancashire Coal-Field. 6. The North 

 Lancashire Coal-Field. 7. The Whitehaven Coal-Field. 



1. The Coal-Field of Northumberland and Durham commences 

 near the mouth of the river Coquet on the north, aud extends nearly 

 to the Tees on the south. As far as Shields the sea is its boundary on 

 the east; from that point it leave* a margin of a few miles between 

 it and the sea, and extends about 10 miles west from Newcastle. Its 

 greatest length is 58 miles, and its greatest breadth about 24 miles. The 

 coal-me-inureo of this field rest on the series of strata of the millstone 

 grit and shale, and are in part under the magnesian limestone, the 

 northernmost point of which is near the mouth of the Tyne. The 

 beds of which this coal formation is composed dip towards the east 

 and crop out towards the west, so that a section of them gives the 

 idea of a form of a boat. In consequence of this disposition the beds 

 of coal in some places appear at the surface, while in the middle of 

 the basiu they are at great depths. At Yarrow, about five miles from 

 the mouth of the Tyne, one of the thickest beds, called the High 

 Main, is 960 feet deep, and rises on all sides; the dip of the strata 

 averages one inch in twenty, but this is not uniform throughout ; and 

 therefore that bed does not rise to the surface at equal distances around 

 Yarrow. The beds of the coal-measures are 82 in number, and consist 

 of alternating beds of coal, sandstone, and slate-clay; making an 

 aggregate thickness of 1620 feet, which varies however in different 

 parts. The irregularities of the surface do not affect the dip or in- 

 clination of the strata ; so that when a valley intervenes they are 

 found in the sides of the opposite hills at the same levels as if the 

 respective strata had once been continuous. It is difficult to deter- 

 mine the exact number of beds of coal, in consequence of the different 

 depths at which the same bed occurs, the numerous faults, and the 

 varying thickness of the beds of coal and other strata. These strata 

 occasionally enlarge and contract so much, that it is only by extensive 

 observation that the identity of the seams can be ascertained. Dr. 

 Thomson supposes the whole number of beds of coal in this field to 

 be twenty-five ; Messrs. Conybeare and Phillips state that forty beds 

 of coal have been Been : a considerable number however of these are 

 wry thin. The two most important beds are those distinguished by 

 the names of High Main and Low Main. The thickness of the 

 first is 6 feet, and of the second 6 feet 6 inches. The Low Main is 

 (bout 60 fathoms below the Hii?h Main. Eight other beds of coal 

 occur between these : one called Bensham is 4 feet thick, and another 

 called Coal- Yard is 8 feet thick. Seven beds of coal have been ob- 

 served under the Low Main, some of which are of considerable 

 thickness, but of an inferior quality. The aggregate thickness of 

 the whole number of seams is about 44 feet ; but there are eleven 

 beds not workable, the thickness of some of them being only a few 

 inches. Five others amount together to only 6 feet. Making proper 

 deductions for these, it may be considered that the available beds 

 amnunt to 30 feet in thickness. 



The number of dykes or faults which traverse fhis field is very 

 considerable. They appear to run in all directions. The most re- 

 markable, called the Gnat Dyk, or 90-foUiom dyk, ha* received the 



latter name because the beds on the north side of it have been thrown 

 down 90 fathoms. Its direction is north-north-east and south-south- 

 west. It enters the sea a little to the south of Hartley, or about three 

 miles north of Shields, and running westward crosses the Tyne at 

 Lemingtou, about four miles west of Newcastle Bridge. In some 

 places it is only a few inches wide, but in Montagu colliery it is 22 yards 

 wide, and is 611ed with hard and soft sandstone. From the southern 

 eide of this dyke two others branch off, one to the south-east and the 

 other to the south-west. The latter, called from its breadth the 

 70-yard dyke, is also filled with hard and soft sandstone. This dyke 

 intersects the upper or Beaumont seam of coal, but does not alter the 

 level on either side. The thickness of the seam however decreases, 

 beginning at the distance of 15 or 16 yards from the dyke : and the 

 coal first becomes sooty, and at length assumes the appearance of 

 coke. The south-eastern branch is only 20 yards in breadth. Another 

 dyke, which passes through Coaley Hill, about four miles west of 

 Newcastle, is about 24 feet wide. It is filled with basalt in detached 

 masses, which are coated with yellow ochre ; a thin layer of indurated 

 clay is interposed between the sides of the fissure and the basalt. 

 The upper seam of coal is here about 35 feet from the surface, and 

 where it is in contact with the dyke is completely charred. Another 

 dyke, which crosses the Tyne at Walker, and traverses the Walker 

 colliery, does not alter the level of the strata, but on each side of it 

 the coal is converted into coke, which on one side in some places was 

 found to be 18 feet thick, and on the opposite side only about 9 feet. 

 At Wai bottle Dean, 5i miles west of Newcastle, a double vein of 

 basalt crosses the ravine in a diagonal direction, passing nearly due 

 east and west ; it underlies at an angle of 78 degrees, and cuts the 

 coal strata without altering their dip, but the seam of coal is charred. 

 A dyke, called the Cockfield Dyke, 17 feet wide, throws up the coal- 

 measures on the south IS feet. The Low Main coal, contiguous to 

 the basalt, is only 9 inches thick, but enlarges to 6 feet at the distance 

 of 160 feet from it; the coal contiguous to the dyke is reduced to a 

 cinder. The dykes, if not large, are locally called trouble*, slipt, or 

 hitches. These minor faults are numerous and extensive, and are a 

 perpetual source of difficulty and expense to the coal-owner by dis- 

 turbing the level of the strata and by the disengagement of carburetted 

 hydrogen gas. They are not however without their use, being often 

 filled with a tenacious water-proof clay, by which numerous springs 

 are dammed up and brought to the surface. The faults which depress 

 the strata have kept valuable seams within the basin, which would 

 otherwise have cropped out and have been lost 



The coal-field of Northumberland and Durham supplies an enor- 

 mous quantity of coal. Besides being consumed in its own district, 

 London depends nearly altogether on it, as well as all the southern 

 coast counties, with the exception of Cornwall. It is consumed along 

 the eastern coast, including all the eastern counties as far west as 

 Hull, Boston, Peterborough, Bedford, and Windsor. An inquiry as 

 to the probable duration of this supply is one of no small interest. 

 Dr. Thomson calculates that this coal-field may fairly be expected 

 to yield coal for 1000 years, at the annual consumption of two 

 millions of chaldrons ; but as we have no data by which to discover 

 how much coal has been already consumed, we cannot tell how much 

 of these 1000 years has already elapsed. Besides this, Dr. Ihomson 

 has taken the average annual consumption much too low for the 

 present time. The coals shipped from the Tyne, the Wear, and the 

 Tees, in 1835, amounted to 4,368,144 tons. The quantity of waste 

 coal is estimated at one-third of the whole. Without therefore taking 

 into account the consumption of the immediate district, the annual 

 quantity of coal taken from the mines is more than 6,552,216 tons. 



On the other hand it appears that in this calculation the area of the 

 coal-field is very much under-estimated, being taken at 1 80 squaremiles. 

 Professor Bucklaud, in his examination before the House of Commons, 

 limits the period of supply at the present rate of consumption to 

 about 400 years. Mr. Baily, in his ' Survey of Durham,' states the 

 period for the exhaustion of the coal to be about 200 years hence. 

 Some proprietors of the coal-mines, when examined before the House 

 of Commons, in 1830, extended the period of exhaustion to 1727 

 years. They assumed that there are 837 square miles of coal strata 

 in this field, and that only 105 miles had been worked out. The small 

 coal taken out of the pits is not considered worth shipment ; large 

 quantities of it were therefore often piled up near the mouths of the 

 pits. These masses of coal wei e frequently set on fire, and burned 

 for several years. Dr. Thomson describes two of these immense fires 

 which were burning in 1814. About three miles to the north of 

 Newcastle, and three miles off the road from Berwick, on the left 

 hand; " one has been burning these eight years. The heap of coal is 

 said to cover twelve acres. The other, on the right hand, is nearer the 

 road and therefore appears more bright : it has been burning these 

 three or four years (1814)." Of late years many more manufactories 

 have been established in this district, by which, and by converting it 

 into coke, most of the small coal is consumed. 



Besides this coal-field there is another coal formation in the northern 

 counties, which is minutely described by Dr. Thomson in the ' Annals 

 of 1'liilosophy,' November, 1814, under the name of the ludependent 

 Coal Formation. This tract terminates westward at Cross Fell, in 

 ('iiinlierland, is supposed to occupy the whole of Durham, and con- 

 stitutes the whole of that part of N orth umber land east of the Cheviot* 



