Cockfield to Botain, situated on the western boundary of the magnesian limestone. Its width is 17 feet at the former place, where it hades to the south, and throws up the coal-measures on that side 8 fathoms. The low main coal contiguous to the basalt is only 9 inches thick, but enlarges to 6 feet at the distance of 50 yards from it. The coal is reduced to a cinder, and the sulphur is sublimed from the pyrites near to the dyke.
I have never been able to trace any of these basaltic veins into the magnesian limestone, and am almost certain that together with the other members of the coal formation, they are covered by it.
Continuing the line of direction of the Cockfield dyke from Botain to the south-east, after passing the eastern boundary of the magnesian limestone, we meet with a dyke on the banks of the Tees a little below Yarm. It there cuts the red sandstone, and continuing its course in the same direction is well known to traverse the north-eastern part of Yorkshire.
Besides the fissures filled with basalt, others of a very different nature intersect the Coal-field. These if large are also called dykes, but, if inconsiderable, troubles, slips or bitches; and are the same that some geologists have called faults.
I have already noticed the main or ninety-fathom-dyke, when speaking of the limestone quarry at Whitley, where it is seen dividing the coal-measures in the cliff, and passing into the sea. It receives its name from the degree of throw which generally attends it in the strata through which it passes, and which are cast down on the northern side about 90 fathoms. At Whitley the same bed of coal which is found at 7 fathoms on the southern side of it, is found at 50 on the northern, the measures being there thrown up on the southern side 43 fathoms. From this point the dyke ranges, though not in a straight line, through that part of
