Taken from The History, Topography, and Directory of the County Palatine of Durham by Francis Whellan. Second edition published in 1894.

In forming a due estimate of the northern coalfields, we must glance at the extent and character of the Coal Measures as they are developed in the different districts; and since the coalfield of Newcastle is historically and commercially pre-eminent, we may start from that centre of activity. On examination of a geological map, it will be seen that, coming south from the Durham coalfield on one side of the central chain of North English hill country and that of Cumberland on the other, a large interval separates them from those of Lancash ire and Yorkshire respectively. It will be seen, too, that there are certain features of connection in each case between east and west, which it is not so easy to establish between north and south, and we may therefore take one division as including the coal regions north of a line drawn from the mouth of the Tees westward through Kendal and the. south side of the Lake country. About equidistant from the Irish Sea on the west and the North Sea on the east rises the broad backbone of the hill country, composed of the Carboniferous Limestone, with all its numerous subdivisions so carefully studied by the lead miners, and bearing on its culminating points, and on the high ground extending for many miles’ breadth on the east, a capping of Millstone Grit. On the west side, or towards Penrith, this main chain has been greatly disturbed and abruptly broken at an early geological period; whilst on the other side, the land slopes more uniformly from the high ground. The strata here inclining gently eastward, partake of the same regularity; and as we proceed towards the coast, succeed in ever ascending order till the various coal-seams "put in" one after the other, and are at length similarly capped by the Magnesian Limestone, and soon afterwards – not cut off but surmounted – by the sea. The field of Blyth, Tyne, and Wear, so called after its rivers, extends from the Coquet on the north to near the Tees on the south for about 50 miles in length, with a breadth of about 20 miles for a great part of the way, till it narrows to a point when it passes north of the Blyth, an area in all of 705 miles. For some miles in breadth along the western side, only a few of the lower seams are worked; then in a line ranging through Newcastle to Durham, we get the full number of the workable seams; and again following a sinuous course from Tynemouth past Houghton-le-Spring to near Bishop Auckland, the overlying Permian formation succeeds, represented by a generally bold outline of Magnesian Limestone resting on the irregular lower red sand, which, from its water-bearing and loose properties, presents great difficulties to the sinking of shafts eastward of this line.

In former days this upper was confounded with the lower (Carboniferous) limestone, and it was supposed that a limit was thus formed to the coalfield on either side. It was therefore a bold step when the Messrs. Pembert on, relying on true geological reasoning, determined to pierce downward from the coast near Sunderland and search for the hidden Coal Measures below. Their famous Monkwearmouth pit was commenced in 1826, and had to pass through 330 feet of this newer formation, towards the bottom of which no less than 3000 gallons of water per minute had to be raised by pumping power. At 285 fathoms they cut the Hutton seam, having previously intersected the Maudlin or Bensham seam 20 fathoms higher. And these resuts appear to establish a curious point in the configuration of the coalfield. The seams which thus lie nearly 1700 feet below the sea at Sunderland occur at a less depth as they pass to the north or to the south, whilst westward they rise to their out-crop at Howes Gill, an elevation of 740 feet above the sea, giving a difference in level of 2440 feet.

It would appear, then, that this is the deepest part or a sort of transverse trough in the stratification; but as the measures have a gentle inclination along the coast, it yet remains to be proved whether the deeper part of the basin does not lie further seaward, and the probability remains of a large area of this productive coalfield extending beneath the German Ocean. At these deep pits and those of Ryhope and Seaham, also sunk within the last few years at a small distance from the coast line, the deeper seams have not yet been reached; but from the sections obtained in the shallower pits in the west, the succession is perfectly well known.

The total thickness of the measures from the lowest known seam upwards may be taken at little more than 2000 feet. The upper half contains only a few unworkable beds, the lower half all the valuable seams. In this field, as in all others, the thickness and character of a particular hand of coal will be found to vary, and that to such an extent as to occasion much difficulty in identifying the seams of distant pits. A coal which is suitable for steam purposes in one part of the area will be found more fitted for household use in another ; and that which is the mainstay of a colliery in one locality, may be barely traceable in another.

The chiefly important seams are the following :—

The average number of seams found to be workable in any one section may fairly be taken as twelve, with about 50 feet of coal in the aggregate.

Great advantages exist in the district; first in the general regularity of the measures dipping at a very moderate angle, commonly about 1 in 20 ; the convenient thickness of the seams, from 3 to 6 feet, the excellent qualities of the coals, and the usual goodness of the roof, which allows of wide working places and roads, with a very small expenditure of timber. The difficulties are the considerable depths of the sinkings in the newer pits, the watery strata to be pierced, and the large amount of fire-damp given off by many of the seams.