principal view, be fulfilled, since I shall have opened a path for others to follow, and traced an outline which some more fortunate observer will with greater ease complete.
The variety of rocks which occurs in this island, as well as the theoretical difficulties in which the connection and order of many of these are still involved, and which are in tome measure at least elucidated by their appearances here, render this island very interesting to the geologist. In attempting to describe them so as to give a clear topographic view of their situations, and at the same time to trace their connections with each other, (that object which is more peculiarly an essential part of geological science,) I have experienced difficulties which other observers must also have felt, and from which I have but imperfectly succeeded in extricating myself. It is to be hoped that our increasing knowledge will at some future day diminish, if not remove, those difficulties, and smooth the path. for the future historians of the earth's surface and structure. In the mean time no greater impediment to the progress of that knowledge of which we are in search can be contrived, than that of assuming a certain regulated order, founded on imperfect and limited, or on prejudiced observations. This proceeding not only renders all investigation nugatory in itself, but accumulates by the establishment and diffusion of false canons, a constantly increasing load of obstruction to the progress of truth. The phenomena which have occurred to me in Scotland, during many years examination of that very instructive country, have so often led to conclusions different from those which have been supposed already established, as to compel my dissent from that system of general rules on which we have hitherto been taught to rely. At the same time, convinced that generalization on this subject was premature, and warned as much by my own discrepancies as by the
