2 Dr. Mac Culloch's Sketch of the 



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 

 thebretical difficulties in which the connection and order of many 

 of these are still involved, and which are in some measure at least 

 elucidated by their appearances here, render this island very inter- 

 esting 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, these difficulties, and 

 smooth the path for the future historians of the earth's surface and 

 structure. In the mean tifne 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 im- 

 perfect and limited, or on prejudiced observations. This proceed- 

 ing not only renders all investigation nugatory in itself, but accu- 

 mulates by the establishment and diffusion of false canons, a con- 

 stantly 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 



