252. This general fact, which I state on much better authority than that of my own observations, viz. on those of Dr Hutton, is not given as absolutely without exception. The theory of whinstone which has been laid down here, leads us indeed to look for some such exceptions. It is certain, that the basis of whinstone, or the material out of which it is prepared by the action of subterraneous heat, is clay in some state or other, and probably in that of argillaceous schistus. It follows, of consequence, that argillaceous schistus may by heat be converted into whinstone, or the material out of which is prepared by the action of subterraneous heat, is clay in some state or other, and probably in that of argillaceous schistus. It follows, of consequence, that argillaceous schistus may by heat be converted into whinstone. When, therefore, melted whinstone has been poured over a rock of such shistus, it may, by its heat, have converted a part of that rock into a stone similar to itself; and thus may now seem to be united, by an insensible gradation, with the stratum on which it is incumbent; and phenomena of this kind may be expected to have really happened, though but rarely, as a particular combination of circumstances seems necessary to produce them. Hence it is evident, that stones may graduate into one another, without being of the same formation; and that it is fallacious to conclude, from the insensible transition of one kind of rock into another, without any other circumstance of affinity, that they have both the same origin. I am disposed, therefore, to make some limitation to what is said in § 72, where I have expressed an absolute incredulity as to such transitions as are here referred to. The great skill and experience of the mineralogist who has described the strata at Scheibenberg, do not allow us to doubt of his exactness, though some of the appearances are such as decomposition and wearing might well enough be supposed to produce. The fairest way is to take Mr Werner's observations just as they are given us, and to try whether they cannot be explained without the assistance of his theory. In effect, the wacken which he describes, rests, it would seem, on an unconsolidated bed of clay; and it may be supposed, that a part of this bed has been converted into wacken by the heat of the incumbent mass, and has thus produced the apparent gradation from the one substance to the other. As the appearances of the rocks of Scheibenberg seem to be considered by Werner as furnishing a very strong, and even an unexpected confirmation of his system, I cannot help thinking, that an explanation of them, on the principles of Dr Hutton, without any straining or forcing of those principles, contributes not a little toward extending the empire of the latter over all the phenomena of geology.