68. To the same excellent geologist we are indebted for the knowledge of an analogous fact, attendant on the passage of whinstone veins through coal strata. As the beds of stone where they are in contact with veins of whin, seem to acquire additional induration, so those of coal, in like circumstances, are frequently found to have lost their fusibility, and to be reduced nearly to the condition of coke, or of charcoal. The existence of coal of this kind has been already mentioned, and considered as a proof of the operation of subterraneous heat. In the instances here referred to, that is, where the charring of the coal is limited to those parts of the strata which are in contact with the whin, or in its immediate vicinity, the heat is pointed out as residing in the vein; and this is to be accounted for only on the supposition of the melted whin, at a period subsequent to the consolidation of the coal, having flowed through the openings of the strata. The heat has been powerful enough, in many cases, to drive off the bituminous matter of the coal, and to force it into colder and more distant parts. Few facts, in the history of fossils, are more remarkable than this, and none more directly assimilates the operations of the mineral regions, with those that take place at the surface of the earth. 69. Again, the disturbance of the strata, wherever veins of whinstone abound, if not a direct proof of the original fluidity of the whinstone, is a clear indication of the violence with which it was introduced into its place. This disturbance of the position of the strata, by shifting, unusual elevation, and other irregularities, where they are intersected by whinstone veins, is a fact so well known to miners, that when they meet with any sudden change in the lying of the _metals_, they are wont to foretell their approach to masses, or veins of unstratified matter; and, in their figurative language, point them out as the causes of the confusion with which they are so generally accompanied.[21] The mineral veins likewise, as well as the strata, are often heaved and shifted by the veins of whinstone. [Footnote 21: A _Trouble_ is the name which the colliers in this country give to a vein of whinstone.]