266. The induration of the sides of these veins, in some cases, has been such, that the sides have become more durable than the vein itself; so that the whinstone has been worn away by the washing of the waves, and has left the sides standing up, with an empty space, like a _ditch_, between them. One of these I remarked on the south side of Brodick Bay, in Arran, which, where it met the face of an abrupt cliff was not less than forty or fifty feet in depth. 267. I shall pass over whatever argument might be drawn in favour of our system, from the slender ramifications of the veins, and the varieties of their sizes, from a few inches to many fathoms in diameter, and also from the connection which they often appear to have with the great tabular masses of basaltes; and shall only add a few remarks on the charring of coal in the vicinity of veins or masses of whinstone. The connection between the charring of coal and the presence of whinstone, was first observed by Dr Hutton; and, as far as opportunities of verifying the observation have yet occurred, appears to be a fact no less general than it is curious and interesting. In the coal mines of Scotland, it certainly holds remarkably, particularly in those about Saltcoats in Ayrshire, where a whinstone dike is known to stretch across the whole of the coal country, and to be every where accompanied with blind or uninflammable coal. At Newcastle, dikes of the same kind are met with, and one, in particular, in what is called the _Walker_ Colliery, has proved the action of subterraneous fire, to the satisfaction of mineralogists nowise prejudiced in favour of the Huttonian system. The coal found under basaltes, in the Island of Sky, has been already mentioned, § 140. To what was said concerning the fibrous structure of the parts of that fossil in immediate contact with the whin, it may be added, that it is also charred in those parts, so as to have hardly any flame when it is burnt, though further down it is of the nature of ordinary coal. Indeed, if there be any truth in Mr Kirwan's general remark, that it is common to find wood coal under basaltes, it must be understood to arise from this, that the coal in contact with the basaltes is frequently charred, and its fibrous structure, by that means, rendered more visible. 268. It has been objected to the supposition of coal having its bituminous part driven off by the heat of the whinstone, that this ought not, on Dr Hutton's principles, to happen in the mineral regions. But it may be replied, as has been done above, that the local application of heat might certainly produce this effect, and might drive off the volatile ports from a hotter to a colder part of the same stratum. The bitumen has not been so volatilized and expanded as entirely to escape from the mineral regions; but it has been expelled from some parts of a mass, only to be condensed and concentrated in others. This supposition coincides exactly with the appearances.