Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/22

 Fell, and Whickham Banks, though no where in the vales of the Tyne and the Team, which severally intersect those elevated portions of land. The conclusion is obvious, that the present irregularity of hill and dale has been occasioned by the partial destruction and dispersion of the uppermost rocky masses, which constitute the coal formation.

That part of the trough in which the greatest thickness of the coal measures is found, seems to lie in the vicinity of Jarrow; and from this point the beds appear to rise to some considerable distance on each side, particularly in a western direction. The average dip of the coal measures is 1 inch in 20; but this inclination is by no means uniform in every part of the district. Thus that seam of coal called the High Main which lies buried at Jarrow, under 160 fathoms of beds of stone, soon rises to the clay in a north-easterly direction, and bassets out in the cliffs between Cullercoats and Tynemouth. In its north-westerly range it reaches Benwell hills, and at Pontop nearly 18 miles due west of the sea shore at Sunderland it is met with at 38$$\scriptstyle \frac 12$$ fathoms from the surface. In a southerly direction it is found at 52 fathoms on Gateshead Fell, but bassets out before it reaches the Wear.

The principal substances besides coal, which constitute the Coal formation, are shale and sandstone; which as they vary in hardness or colour receive different provincial names from the miners. It is not possible to discover in the Coal measures any regular order of succession, which will apply to the whole Coalfield, and it is even with difficulty that in very limited portions of it the continuity of particular seams can be traced. This arises from the variable thickness and the rapid enlargement and contraction of the different beds; that which in one section is scarcely perceptible, having attained in a neighbouring pit the thickness of several fathoms. It is