The strata of the coal district are extensively fractured and displaced by dykes or faults, which run across the country in a direction nearly parallel to each other from east to west. The principal of these is known by the name of the Ninety-fathom Dyke. It runs from near Cullercoats in the direction indicated upon the plan by a strongly marked red line, passing about four or five miles northward of Newcastle, and in all probability going to the western ocean. The coal strata on the north side of this dyke may be traced for twenty miles, thrown downwards from sixty westward to 150 fathoms eastward, near the sea, and hence the name by which this great fault or slip in the strata has been distinguished.

The Ninety-fathom Dyke may be traced at Whitley, Killingworth, Kenton, Denton Hall, Lemington, Stella Hall, Stevens' Hall, Greenside, Kyo, East of Coalburn, South of Minsteracres, and through the Lead Mines belonging to W. B. Beaumont, Esq., M.P., towards the western ocean.

It has been drifted through at Shire Moor, and from the south to the north side at Gosforth, Bell's Close (near Lemington Iron Works), at East Towneley, Stella Colliery, and West Towneley Colliery, about half a mile west of Greenside, on or under the road from Greenside to Coalburn.

The drift at Bell's Close was commenced by Mr. Christopher Bedlington, agent to the Montague Family, about seventy years ago, and hence it is called " Kitty's Drift." It was intended to cut several seams of coal in the neighbourhood of Kenton, on the level it was commenced at, which was very little above that of the Tyne at Bell's Close; it was likewise intended to use it as a horse way for the purpose of bringing the coal and water out on the level without incurring the great expense of sinking a shaft and drawing the same up by an engine, a mile northward of the dyke. It was known, that for a considerable distance the seams of coal, even north of the dyke, had been worked above the Tyne level, and that unworked coal seams would still be found further to the dip, where this level road was intended to end, and north-eastward beyond these seams to the rise.

On reaching a certain point, however, after many years of tedious labour, and the expenditure of a large sum of money, it was discovered that, in consequence of faults and troubles, the coal seams were thrown downwards to the north about forty fathoms below the level of this drift, and could not be reached in the way contemplated. Some time after this, pits were sunk to the coal north of the dyke; and the water from them is at present pumped into "Kitty's Drift," through which it is discharged into the river Tyne. This is a remarkable instance of the misadventure and miscalculation of mining engineers in former times.

It may be remarked, that it was in this district that iron bars were first used as edge rails for tram or railroad carriages. Benwell, in the same neighbourhood, was probably the first place where coal was worked in Great Britain.

It was on Wylam Colliery railway, which terminates at Lemington, that locomotives were either first or very early used on metal rails of various forms of construction to suit the rough and rugged road existing at that day. The engines had wheels constructed to suit the rails; these wheels and rails have since undergone changes, having been three or four times re-modelled, till they have become what are now generally in use on all railways.

In the village of Benwell, which is pleasantly situated on the north bank of the river Tyne, commanding a picturesque view of the country for several miles to the south and west, up the valleys of the Tyne, Ravensworth, Team, and Derwent, the remains of my late friend, Mr. John Buddle, are interred in a vault constructed during his life time, in the escarpment of a coal seam on the south side of the church-yard. Appropriate locality for the last earthly resting place of one who had devoted a long life to the interests of the coal trade.

Several centuries ago coals were conveyed in carts from Brandon, near Brancepeth, and the late Lady Peat's collieries at Thornley Common, to iron works then established on a small scale on the Tyne and Wear. The distance was upwards of twenty-four miles, and several pits, where good coals were worked, had to be passed in making the journey. The reason why coals from the more distant pits were selected over others that might have been obtained nearer, was, no doubt, their being found preferable for the purposes to which they were to be applied. This fact proves that, even at that early period, when the coal and iron trades were in their infancy, the parties engaged in them had discerned and appreciated the quality of coal best suited for such manufacture. It is fortunate for the iron manufacturers of the present day that they can obtain ample supplies of suitable coal on so much more favourable conditions than their predecessors.

A considerable basaltic dyke, visible on the surface at Brockley Whins, proceeds thence across the Tyne at Walker, through Byker Bar, the Town Moor, to Kenton, where it meets the Ninety-fathom Dyke, on the north side of which it makes its appearance in two divisions a mile apart. The southernmost division runs from East Kenton Hall, taking the course of the Roman Wall, to Heddon-on-the-Wall, near which village we find even upon high ground the escarpment of the lowest seam of coal.

The northern division passes through Coaly Hill, where it is 24 feet in thickness, which is worked in quarries for the purpose of road making.

Five or six other basaltic dykes intersect the coal-field at various places in Northumberland, to the north of the Ninety-Fathom Dyke. Two of them run parallel about half a mile apart, from Hartley to about a mile north of Cramlington. Two others run westward from the sea near Blyth, one on each side of the harbour, about a mile and a half apart. These are all nearly parallel to each other, and also to the one previously described from Brockley Whins to Coaly Hill. Another basaltic dyke, near to Radcliffe Colliery, runs about east and west. At this point from the sea westward, the coal field is only about four miles in breadth. Three miles north of Radcliffe is Amble Harbour on the Coquet, where this outcrop of coal enters the sea.

The Heworth Dyke extends from the sea, south of Jarrow, by Heworth, Swalwell, Axwell Park, west of Stella, to Stevens' Hall, where it disappears in the Ninety-fathom Dyke. On the north or opposite side of which, and nearly in a line with the Heworth Dyke, a similar dyke runs close by the house occupied by the agent of the Towneley Colliery, at the west end of Ryton Bar Moor, and north west through Crawcrook fields. It then crosses the Tyne, under the house in which the late eminent engineer, George Stephenson, Esq., was born, about half a mile below Wylam, enters the Rift estate, and continues through the Wylam estate to Horsley Wood, where the Brockwell seam of coal, there called the "Crankey," and sometimes the "Horsley Wood Seam" terminates at the surface. This is the lowest workable seam in the coal series, and it takes its name from its coming to the surface at Brockwell Woods, in Blaydon Burn, below Barlow.

The Hett Basaltic Dyke, in the county of Durham, traverses the coalfield from Easington, between Shotton and Haswell Collieries, also between Thornley and Ludworth by Hett, between Sunderland Bridge and Ferry Hill, close by the north end of the village of Tudhoe, crossing the Wear, and is seen a little north of the Willington Colliery near Brancepeth, apparently running into the Butterknowle Slip Dyke. Further westward, these two and the Cockfield Fell Basaltic Dyke appear to come to a point altogether, and thence on towards the Western Ocean. The Hutton seam of coal, on the south side of this dyke, is much thinner and more expensive to work than the same seam on the north side of it, particularly in the eastern portion of the district. This dyke may be traced considerably beyond the out-crop of the coal at Witton-le-Wear, beyond which place it runs nearly parallel with the out-crop to Woodland Colliery, a distance of nearly six miles, which colliery is situated about two miles to the south of the Hett Dyke, at the extreme out-crop, and at about the same distance northward from the Cockfield Fell Dyke. These three dykes approach each other as they proceed westward; the reverse is the case as they go eastward, the Hett Dyke running into the sea near to Easington, and the Cockfield Dyke running between Great Aycliffe and Darlington, close to Roseberry Topping on the south, into the sea at Whitby. In the same manner that the Hett Dyke deteriorates the quality of the Hutton seam southward of it, does the Cockfield Fell Dyke deteriorate the quality of the ironstone to the south of it, which is particularly observable in the neighbourhood of Roseberry Topping.

The Hett Dyke has been drifted through at Shotton, which pit was sunk by the Haswell Company on the south side of the dyke for the purpose of working a good Five-quarter seam, and also in expectation of meeting with the Hutton seam in good workable condition. The Haswell Pit had been sunk previously north of the dyke, into a good Hutton seam, the produce being shipped by the Durham and Sunderland Railway at Sunderland, and it was intended to convey the coal south of the dyke from Shotton Colliery by the Hartlepool Railroad to Hartlepool Dock for shipment. When the Hutton seam was sunk to at Shotton, it was found to be very inferior in consequence of its being tender. The Five-quarter was, therefore, mainly resorted to, and the proprietors afterwards bored or sunk to the Beaumont or Harvey seam below the Hutton. They then made a drift in the Hutton seam to the Hett Dyke, which they found to be of great thickness, and very hard, and after much labour and expense they pierced through it into the good Hutton seam, on the north side, thus enabling a direct underground communication between the Shotton and Haswell Collieries to be made at some future day, and so admitting of the good Hutton coal being brought through a long lead in this underground drift up the Shotton Pit, and led and shipped along with the Five-quarter seam at Hartlepool.

The quality of the Hutton seam on the south side of the Hett Dyke had been proved previously by another proprietary, the Thornley Company, who, in consequence of its thinness, limited the workings to the Fivequarter; and subsequently sunk to the Beaumont or Harvey, which they found to yield good coking coal. The Thornley Company being in possession of a large district north of the dyke, drifted up to, but did not at that time attempt to cut through the dyke, but sunk another pit at Ludworth, where they found the Hutton seam in excellent condition, which they now work extensively. The coals from Ludworth and Thornley Colliery being sent to Hartlepool Docks.

The Hett Dyke was likewise cut through at Willington, near Brancepeth.

The Butterknowle Forty-fathom Slip Dyke is seen at Cockfield Fell, a little west of Cockfield, and proceeds by Thrislington, Bishop Auckland, Ferry Hill Station, and near Monkhesleton, to the sea. It runs parallel to the Hett Dyke throughout its course, at an average distance of about three miles to the south of it. This is a slip dyke and not a basaltic one like those of Hett and Cockfield Fell, but like the Ninety-fathom Main Dyke and the Heworth Twenty-five-fathom Slip Dyke.

There are several small dykes and slips met with in various parts of the coal-field, running in different directions, which are of sufficient importance to call for minute description. These dykes cause great expense to coal owners, as they interrupt the working of the coal very materially.

The present paper being foreign to the purpose, it is not necessary to express any opinion as to the formation of these extraordinary phenomena, further than to say that it would appear some great force had occurred, throwing the stratified crust of the earth down in some places and up in others. As regards the basaltic dykes, there would seem to have been a severance of the strata in a vertical or sloping direction, in many places several yards apart, and the intervening space to have become filled with basalt, while in a state of fusion from intense heat. At Cockfield this severance extends to about 22 yards; it is greater at Shotton and westward. At Willington, near Brancepeth, the dyke is not so difficult to penetrate as at other places.

The fact of the severance having become filled up with basalt in a state of fusion is evident from the circumstance of the coal in some places, on both sides of these dykes, having been found charred or converted into coke by the agency of heat, and deteriorated from other causes.

At Stella Pit we meet with a coal which when burnt in a coke oven for 150 hours does not change its appearance. In certain districts, also, the quality of coal in the neighbourhood of these dykes is found to be deteriorated, from what cause has not been satisfactorily ascertained.

A similar deterioration, as before remarked, occurs with respect to the ironstone south of Cockfield Fell Dyke.

A peculiar dyke or fault is found running in a direction north and south, extending from near the City of Durham to the Team and King's Meadows, on the Tyne. It is 27 fathoms in depth in some places, and is filled with alluvial deposits, pointing in a direction towards Norwood Colliery, on the Team valley, and through Ravensworth Park.