416 Book III. Chap. III. Coal , and asbciaied beds.

In the Marquis of Anglesea’s park, called Beaudesert, thereis a mine of caunel coal, which is reserved for the exclusive useof the Marquis’s family. This coal has a brownish-black colour,and much less lustre than common coal. The fracture is flatconchoidal, and quite smooth ; but the cross fracture is morerough, and on that account has a blacker appearance. Thiscoal is hard, and does not soil the fingers. Interspersed throughit are numerous specks of a brown matter, very similar inappearance to Bovey coal.

Many faults occur in the coal-field. They are rents in thebeds, which are usually filled with clay. Very frequently theheight of the beds varies on the two sides of a fault. By a greatfault which occurs near Bilston, the dip of the coal is reversed ;that is to say, the coal-beds on the south side of the fault dipsouth, and those on the north side dip north. But this is anunusual occurrence.

Ironstone is found in several of the measures. But of thesetwo only are worked for the ore. Vegetable impressions arecommon. The deepest pits are sunk about 140 yards.

Millstone-grit does not appear to have been noticed in thisdistrict; but the coal-shales repose immediately on the lime-stone.

Neither does the subjacent limestone itself belong to thesame formation with that constituting the ordinary basis of theother coal-fields; but appears to be of much higher date, agree-ing closely in its extraneous fossils and general character withthe transition limestone which (as we shall have an opportunityof demonstrating hereafter) is separated from the mountainlimestone by the important formation of the old red sandstone.The limestone of Dudley and Walsall will therefore be describedin treating of the transition rocks.

This absence of millstone-grit, carboniferous limestone, andold red sandstone, and the immediate contiguity of the coal-measures and a transition rock, constitute a remarkable andimportant character in this coal-field : and in this it resemblessome others in Shropshire , of which we shall hereafter haveoccasion to speak.

A little on the west of Dudley there is a considerable tractin which some of the collieries having taken fire from spon-taneous ignition, many years back, the conflagration has spreadto a great extent, and still continues in great activity : thisproduces many singular effects: smoke and steam may in someplaces be observed to rise; the vegetation on the surface isaccelerated, and the ponds become thermal : where the ignitedmass of coal has been nearer the surface, the argillaceous strata