At Whitehaven, the principal entrance to the coalmine, both for men and horses, is by an opening at the bottom of a hill, through a long passage hewn in a rock. This, by a steep descent, leads to the lowest bed of coal. The greatest part of the descent is through spacious galleries, which intersect other galleries; all the coal having been cut away, except large pillars, which, in deep parts of the mine, are three yards high, and about twelve yards square at the base, such great strength being there required to support the ponderous roof. There are three distinct and parallel strata of coal, which lie at a considerable distance above each other, and which have a communication by pits that are sunk between them. These strata are not always regularly continued in the same plane. The miners occasionally meet with veins of hard rock, which interrupt their further progress, and, at such places, the earth, on one side of the vein, appears to have sunk down, while that on the opposite side has its ancient situation. These breaks the miners call _dykes_ (4). When they come to one of them, their first care is to discover whether the coal, in the part adjoining, be higher or lower than that in which they have been working; or, to use their own terms, whether it be cast down or cast up. For this purpose they examine attentively the mineral strata on the opposite side, to see how far they correspond with those which they have already passed through. If the coal be cast down, they sink a pit to it: but if it be cast up, the discovery of it is often attended with great labour and expense. In general the entrance to coal mines is by perpendicular shafts, and the coals and workmen are drawn up by machinery. As the mines frequently extend to great distances, horizontally, beneath the surface of the earth, peculiar care is necessary to keep them continually ventilated with currents of fresh air, for the purpose, not only of affording to the workmen a constant supply of that vital fluid, but also to expel from the mines certain noxious exhalations which are sometimes produced in them.