a rock in a condition to be bent and incurvated, should by a peculiar application of external force admit of that more continued prolongation which in certain circumstances would produce a vein. The analogous incurvations indeed, and the evident prolongations which take place among the laminæ of mica slate, and in the contorted veins of granite and quartz which traverse them, offer cases of parallel difficulty. If the solution which I have offered be incompetent to this purpose, it is only one more added to the numerous unexplained phenomena which are to be found attending the subject of geology wherever we turn our regards: for we can then look to neither of the prevalent hypotheses for an adequate explanation of this case; the mechanical structure of the schist as indicated by the parallel disposition of the mica, combined with the want of similar mechanical arrangement in the vein, offering a difficulty to the one as great as it is to the other. I speak of a mechanical arrangement in the schistose rocks as if it were admitted by all, because it appears a circumstance attending on many of these rocks, as perfectly demonstrated as any thing of which we have not actually witnessed the creation, can be demonstrated to our senses.
For the same reasons I speak without hesitation of the displacement, fracture, and incurvation of the graywacké which is imbedded in the trap, and in so doing it is not my wish to speak the language of an hypothesis, but to describe a fact, in such terms as can alone convey an adequate notion of the appearances to a mind divested of all hypothesis. If Nature has really produced imitations of mechanical arrangement by processes unknown to us, it is to be wished that the mode in which they have been produced may be shown, either by means of experiments, or by analogies drawn from that science of which the laws regulate the great proceedings
