Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/38

 vein, it appears to be divided into a number of small branches, some of which are upcasts and some down casts, which break and rend the coal-measures to the width of 200 yards. In the Wear water mines it is an upcast on the northern side of 30 fathoms.

The Thistle pit dyke which is a downcast of eight fathoms to the south, and traverses the Coal-field from west to east, appears to have been as well known to the miners who lived nearly a century since, as to those of the present day. It was the southern limit of the ancient colliery situated at Heaton and Benton banks, and by perforating it the mine at Heaton was inundated on the 3d of May, 1815, when the viewer and seventy-four men and boys lost their lives. — For an account of this catastrophe, see Monthly Magazine and Philosophical Journal.

The Heworth dyke is an upcast on the southern side of 25 fathoms, and from the vicinity of Falling hall it stretches towards the west, and enters the main dyke at Ryton. The high-main coal to the south of this dyke is said to lose a strong parting known by the name of Heworth band.

At Hebburn, Oxclose, Ravensworth, Lambton, Newbottle, Lumley, Raynton, and every other colliery worked in the district, similar dykes occur; and, following the same law as the veins of the Lead-mine district, they elevate the strata on that side towards which they dip.

Whatever be the throw or difference of level occasioned in the coal-measures by these dykes, it never happens, as might be expected, that a precipitous face of rock is left on the elevated side; or that the lower side is covered by an alluvial deposit, which connects the inequality of the beds that are in situ; but the surface of the ground covering the vein is rendered level by the absolute removal of the rocky strata on the elevated side. The same phenomena have been